Midday Exposure Research Articles

Bright Light Therapy in the Morning or at Mid-Day in the Treatment of Non-Seasonal Bipolar Depressive Episodes (LuBi): Study Protocol for a Dose Research Phase I / II Trial.

ObjectiveThis study protocol aims to determine, using a rigorous approach in patients with bipolar disorder (BD) and non-seasonal major depressive episode (MDE), the characteristics of bright light therapy (BLT) administration (duration, escalation, morning and mid-day exposures) depending on the tolerance (hypomanic symptoms). MethodsPatients with BD I or II and treated by a mood stabilizer are eligible. After 1 week of placebo, patients are randomized between either morning or mid-day exposure for 10 weeks of active BLT with glasses using a dose escalation at 7.5, 10, 15, 30 and 45 minutes/day. A further follow-up visit is planned 6 months after inclusion. Patients will be included by cohorts of 3, with at least 3 days of delay between them, and 1 week between cohorts. If none meet a dose limiting toxicity (DLT; i.e hypomanic symptoms), the initiation dose of the next cohort will be increased. If one patient meet a DLT, an additionnal cohort will start at the same dose. If 2 or 3 patients meet a DLT, from the same cohort or from two cohorts at the same dose initiation, the maximum tolerated dose is defined. This dose escalation will also take into account DLTs observed during the intra-subject escalation on previous cohorts, with a “Target Ceiling Dose” defined if 2 DLTs occured at a dose. DiscussionUsing an innovative and more ergonomic device in the form of glasses, this study aims to better codify the use of BLT in BD to ensure a good initiation and tolerance. Trial registrationClinicalTrials.gov Identifier: NCT03396744.

Brief hyperopic defocus or form deprivation have varying effects on eye growth and ocular rhythms depending on the time-of-day of exposure

It is generally accepted that myopic defocus is a more potent signal to the emmetropization system than hyperopic defocus: one hour per day of myopic defocus cancels out 11 h of hyperopic defocus. However, we have recently shown that the potency of brief episodes of myopic defocus at inhibiting eye growth depends on the time of day of exposure. We here ask if this will also be true of the responses to brief periods of hyperopic defocus: may integration of the signal depend on time of day? If so, are the rhythms in axial length and choroidal thickness altered? Hyperopic defocus: Birds had one eye exposed to hyperopic defocus by the wearing of −10D lenses for 2 or 6 h at one of 3 times of day for 5 days: Morning (7 am – 9 am: n = 13; 7 am – 1 pm: n = 6), Mid-day (12 pm – 2 pm: n = 20; 10 am – 4 pm: n = 8), or Evening (7 pm – 9 pm: n = 12; 2 pm – 8 pm: n = 11). A separate group wore monocular lenses continually as a control (n = 12). Form deprivation: Birds wore a diffuser over one eye for 2 h at one of 3 times of day for 5 days: Morning (n = 12); Mid-day (n = 19) or Evening (n = 6). For all groups, ocular dimensions were measured using high-frequency A-scan ultrasonography at noon on the first day, under inhalation anesthesia. On day 5, eye dimensions were re-measured at 12 pm, and refractive errors were measured using a Hartinger's refractometer. A subset of birds in the 2-h lens group (morning, n = 8; mid-day, n = 8; evening, n = 6), and the deprivation group (n = 6 per time point), were also measured at 6 pm, 12 am, 6 am and 12 pm on the last day of exposure, to obtain the parameters of the diurnal rhythms in axial length and choroidal thickness. The effects of 2 h of defocus depended on time of day of exposure: it stimulated eye growth when exposure was in the morning and inhibited it when it was at mid-day (change in vitreous chamber, X-C; ANOVA p < 0.0005; 120 μm vs −77 μm/5d, respectively; t-tests: p = 0.001; p = 0.01; post-hoc tests: p = 0.002). For mid-day, experimental eyes were more hyperopic (1.4 D; p < 0.0001). Similar to 2 h defocus, 6 h exposures at mid-day inhibited growth and produced hyperopia (X-C: −167 μm; t-test p = 0.005; RE: 1.8 D; p = 0.03). The effects of 2 h of FD were similar to those of hyperopic defocus in inhibiting growth for mid-day exposures, but FD inhibited growth for the morning exposures as well (Axial length: X-C: Morning: −122 μm; mid-day: −92 μm; ttests p = 0.006 and p = 0.016 respectively). Experimental eyes were more hyperopic (1.8 D; 1.0 D; p < 0.05). The rhythms in axial length were altered for the morning exposures in both conditions. Form deprivation in the morning, which caused inhibition, caused the phases of the two rhythms to shift toward one another (peaks at 6:00 am and 10:45 am for choroid and axial length respectively). Our findings imply that the retinal “integrator”, and/or scleral growth regulator exhibit diurnal rhythms. Furthermore, they suggest that reading activities early in the day may be contraindicated in school children at risk of becoming myopic.

Estimating latitudinal variability in extreme heat stress on rocky intertidal shores

AbstractAimBroad‐scale patterns of heat stress play an important role in shaping the geographical distributions of many species and may differ from large‐scale changes in average temperatures. For species living on rocky intertidal shores extreme heat stress occurs when hot dry aerial conditions coincide with midday low tides. We used empirical and modelled temperature data, and estimates of cumulative aerial exposure and solar radiation, in order to test the hypothesis that heat stress on Australian rocky intertidal shores decreases with increasing latitude.LocationRocky intertidal shores of south‐eastern Australia spanning &gt; 1500 km and 13° of latitude (26°24′23″ S to 39°07′47″ S).MethodsIn situ temperature measurements, hourly tidal elevations and daily solar radiation taken over three consecutive summers (December 2009–February 2012) were used to quantify latitudinal variability in extreme heat stress, cumulative aerial exposure and solar radiation, respectively. Comparisons between hourly in situ temperatures and meteorological data were used to produce a large‐scale statistical model capable of estimating intertidal substratum temperatures during daytime low‐tides, which was then extrapolated across 22 locations.ResultsHeat stress estimated using in situ loggers deployed across five east coast locations typically did not decline with increasing latitude and neither did midday exposure or solar radiation. The meteorological model proved to be a successful method for estimating rocky shore heat stress and in contrast to the empirical data displayed strong latitudinal trends in mean daily maxima and cumulative heat stress. Modelled acute heat stress (i.e. summer maxima), however, did not decline with increasing latitude, as there was greater thermal variability at higher latitudes.Main conclusionsThe meteorological model developed in this study represents a useful approach for estimating broad‐scale patterns of heat stress on rocky intertidal shores. Results also indicate that latitudinal patterns of acute and chronic heat stress may differ from average temperatures, which are commonly assumed to decline with increasing latitude. Such broad‐scale patterns of thermal stress as described in this study will significantly contribute to our ability to understand the impact of climate change on vulnerable rocky intertidal communities.

Photoinhibition of photosynthesis in leaves of grapevine (Vitis vinifera L. cv. Riesling). Effect of chilling nights

Photoinhibition of photosynthesis was investigated in control (C) and chilling night (CN) leaves of grapevine under natural photoperiod at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) and photosynthetic electron transport measurements. When the potential efficiency of photosystem (PS) 2, Fv/Fm was measured at midday, it markedly declined with significant increase of F0 in CN leaves. In isolated thylakoids, the rate of whole chain and PS2 activity were markedly decreased in CN leaves than control leaves at midday. A smaller inhibition of PS1 activity was also observed in both leaf types. Later, the leaves reached maximum PS2 efficiencies similar to those observed in the morning during sampling at evening. The artificial exogenous electron donors diphenyl carbazide, NH2OH, and Mn2+ failed to restore the PS2 activity in both leaf types at midday. Thus CN enhanced inactivation on the acceptor side of PS2 in grapevine leaves. Quantification of the PS2 reaction centre protein D1 following midday exposure of leaves showed pronounced differences between C and CN leaves. The marked loss of PS2 activity in CN leaves noticed in midday samples was mainly due to the marked loss of D1 protein of the PS2 reaction centre.

Effects of solar radiation on dimethylsulfide cycling in the western Atlantic Ocean

The influence of solar radiation on springtime rates of photochemical and biological consumption of dimethylsulfide (DMS) in surface waters from the western Atlantic Ocean was examined by exposing 0.2 μm filtered and unfiltered surface seawater to natural sunlight at five depths in the upper 30 m. Parallel deck incubations of 0.2 μm filtered seawater under various long-pass optical filters were also carried out to aid in assessing the wavelength dependence of DMS photolysis. DMS photolysis rate constants for mid-day exposure (∼10:30–17:30 local time) to surface irradiance ranged from 0.026 to 0.086 h −1 and were highest in coastal and shelf waters. Photolysis rate constants decreased with increasing irradiation depth, in accordance with the attenuation of ultraviolet radiation (UVR, 280–400 nm). Total DMS consumption rates (photochemical+biological) in unfiltered surface samples also decreased with increasing incubation depth and were larger than photolysis rates at nearly all depths and all stations. The decrease in photolysis rate constants with exposure depth was mirrored by biological DMS consumption rate constants that were severely inhibited at surface irradiances, and approached or exceeded dark rate constants at deeper exposure depths. Photolysis rates were 2–19 times greater than estimated biological consumption rates in the surface light exposed samples, while biological consumption rates were significantly larger than photolysis rates at incubation depths below the 1% light level for UV–B radiation (280–320 nm). Total DMS loss rates increased up to nine-fold with UVR exposure, but changes in DMS concentrations were not strongly correlated to light dose, presumably due to parallel, light-mediated DMS production processes. The primary loss process for DMS depended mainly on the depth interval considered and the attenuation of UVR; in general, photochemical removal dominated shallow layers characterized by high UV–B intensities, whereas biological removal dominated in deeper layers where UV–B was absent, but UV–A (320–400 nm) and visible (400–700 nm) light fluxes were still relatively high. These results demonstrate that UVR exposure significantly influences the spatial and temporal pattern of DMS production and loss processes, and ultimately the DMS flux to the atmosphere.

Photoinhibition and Recovery of photosystem 2 in Grapevine (Vitis vinifera L.) Leaves Grown Under Field Conditions

Photoinhibition of photosynthesis was investigated in grapevine (Vitis vinifera L.) exposed to 2 or 4h of high irradiance (HI) (1 700-1 800 &mu;mol m-2 s-1) leaves under field conditions at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) and photosynthetic electron transport measurements. When the photochemical efficiency of photosystem 2 (PS2), Fv/Fm, markedly declined, F0 increased in both 2 (HI2) and 4 h (HI4) HI leaves sampled at midday. When various photosynthetic activities were followed on isolated thylakoids, HI4 leaves showed significantly higher inhibition of whole chain and PS2 activity than the HI2 leaves sampled at midday. Later, the leaves reached maximum PS2 efficiencies similar to those observed early in the morning during sampling at evening. The artificial exogenous electron donor Mn2+ failed to restore PS2 activity in both variants of leaves, while DPC and NH2OH significantly restored PS2 activity in HI4 midday leaf samples. Quantification of the PS2 reaction centre protein D1 and 33 kDa protein of water splitting complex following midday exposure of leaves showed pronounced differences between HI2 and HI4 leaves. The marked loss of PS2 activity noticed in midday samples was mainly due to the marked loss of D1 protein in HI2, while in HI4 it was mainly 33-kDa protein.

Effects of ultraviolet radiation on Laminaria saccharina in relation to depth and tidal height in the Gulf of Maine

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 256:75-85 (2003) - doi:10.3354/meps256075 Effects of ultraviolet radiation on Laminaria saccharina in relation to depth and tidal height in the Gulf of Maine Amy M. Apprill1,3,4, Michael P. Lesser2,3,* 1Department of Marine and Environmental Science, University of San Diego, San Diego, California 92110, USA 2Department of Zoology and Center for Marine Biology, University of New Hampshire, Durham, New Hampshire 03824, USA 3Shoals Marine Laboratory, G14 Stimson Hall, Cornell University, Ithaca, New York 14853, USA 4Present address: School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822, USA *Corresponding author. Email: mpl@cisunix.unh.edu ABSTRACT: The effects of solar radiation, both visible and ultraviolet (UV-R, 290 to 400 nm), on the kelp Laminaria saccharina (L.) Lamour were examined in relation to depth distribution and tidal height in the Gulf of Maine. Despite the high attenuation of visible and UV-R, shallow subtidal L. saccharina exhibited significant decreases in midday measurements of steady-state quantum yields of Photosystem II (PSII) fluorescence compared to deeper conspecifics. Decreases in PSII quantum yields under low-tide conditions at midday were more pronounced and associated with higher coefficients of non-photochemical quenching than yields of the same algae measured at midday under high-tide conditions. Steady-state quantum yields in shallow algal populations had not recovered by early morning of the following day. Laboratory experiments were conducted to partition out the effects of high visible radiation versus UV-R effects on steady-state quantum yields observed in the field. Algae exposed to solar visible PAR (photosynthetically active radiation; 400 to 700 nm), PAR + UV-A (ultraviolet-A radiation; 320 to 400 nm), and PAR+UV-A+UV-B (ultraviolet-B radiation; 290 to 320 nm) treatments exhibited daily midday depressions in steady-state quantum yields, similar to those observed in field samples at low tide. The PAR+UV-A+UV-B treatment showed a significantly greater depression in PSII quantum yields than field samples at low tide, and took longer to recover at night. Algae exposed to the UV-R component of the spectrum also showed a significant decrease in gross primary production and contained less areal chlorophyll a than field samples, while non-photochemical quenching (a measurement of the dissipation of excess excitation energy) was significantly higher during midday exposures to UV-B. Significantly greater concentrations of the UV-B-absorbing compound mycosporine-glycine, a mycosporine-like amino acid (MAA), were present in the shallow field and experimental PAR+UV-A+UV-B-treated algae. Our results suggest that exposure to midday visible irradiances resulted in dynamic photoinhibition, while exposure to visible and UV-R irradiance in the Gulf of Maine results in both dynamic and chronic photoinhibition that causes a decrease in gross primary production of L. saccharina in shallow waters or under low-tide conditions. KEY WORDS: Macroalgae · Chlorophyll fluorescence · Laminaria saccharina · UV-B radiation · Photoinhibition · Mycosporine-like amino acids · Gulf of Maine Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 256. Online publication date: July 17, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Photoinhibition of Photosynthesis in Vitis berlandieri and Vitis rupestris Leaves under Field Conditions

Photoinhibition of photosynthesis was investigated in Vitis berlandieri and Vitis rupestris leaves under field conditions at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) and photosynthetic electron transport measurements. When the photochemical efficiency of PS2, Fv/Fm, markedly declined, F0 increased significantly in leaves of V. berlandieri, while F0 did not increase in V. rupestris leaves. Isolated thylakoids of leaves of V. berlandieri showed significant inhibition of whole chain and PS2 activities at midday. A smaller inhibition was observed for V. rupestris. Later, the leaves reached maximum PS2 efficiencies similar to those observed early in the morning during sampling at evening. The artificial exogenous electron donor Mn2+ failed to restore PS2 activity in both species, while DPC and NH2OH significantly restored PS2 activity in V. rupestris midday leaf samples. Quantification of the PS2 reaction centre protein D1 and 33 kDa protein of water splitting complex following midday exposure of leaves showed pronounced differences between V. berlandieri and V. rupestris leaves. The marked loss of PS2 activity noticed in midday samples was mainly due to the marked loss of D1 protein in V. berlandieri while in V. rupestris it was the 33 kDa protein.

Measurements of JNO 3− in snow by nitrate-based actinometry

Chemical actinometry was used to measure nitrate photolysis rate coefficients, J NO 3 − , on and in snowpack at Summit, Greenland. Sealed glass tubes containing nitrate and a hydroxyl radical trapping system were buried in snow and exposed for between 2 and 24 h. Average J NO 3 − values for 2-h midday exposures in early June on surface snow were 10–14×10 −7 s −1. Averages over 24 h were 3.5–4.5×10 −7 s −1. These values reflect the integrated photon flux and also any variation of the nitrate photolysis rate with temperature. Attenuation of J NO 3 − within the firn was 0.03–0.04 cm −1 for 24-h exposures and 0.08 cm −1 for a 2-h exposure. Different attenuation coefficients may relate to differential light penetration due to changes in sun angle over the course of 24 h.

Out in the midday Sun: Risk behaviour and optimistic beliefs among residents and visitors on tenerife

A questionnaire was distributed to 107 local residents on a beach on the island of Tenerife and to 108 visitors from Britain and continental Europe. Measures included perceived danger of sun exposure. environmental concern. value of a suntan, optimism regarding personal risk of skin damage relative to others of one's age and gender, amount of midday sun exposure, sunscreen use and skin type. Use of sunscreen protection was greatly below recommended levels, though higher for women (N = 103). Among visitors, the British (N = 54) showed the riskiest behaviour. Relationship between behaviour. beliefs and background variables varied between groups. Overall there was a significant optimistic bias. This was stronger for the British, and for men. The relationships between optimism and other measures varied between the different national groups. In particular, among the British. greater optimism was associated with placing a higher value on a suntan, with having a more sensitive skin type, with using less adequate sunscreen protection, and with spending a (nonsignificantly) greater proportion of time exposed to the sun in the middle of the day. Among locals and visitors from continental Europe, optimism was associated with less midday exposure. It is concluded that these data offer evidence for two complementary interpretations of the relationship between optimism and health behaviour. On the one hand, those who perceive themselves to be at greater risk may be motivated to take more precautions. while risk-taking may be greater among those regard themselves as less vulnerable. On the other hand. those who take more precautions may infer that their own relative risk is lower. It is argued that research should not assume a single process relating perceived risk to behaviour, but consider factors that might predict the relative importance of alternative processes.

Midday exposure to bright light changes the circadian organization of plasma melatonin rhythm in humans

Effects of bright light exposure at midday were examined on plasma melatonin rhythm in humans under controlled living conditions. Bright light of 5000 lx was provided from the ceiling at midday (1100–1700 h) for 3 consecutive days and the circadian rhythm in plasma melatonin was determined from the fourth to fifth day. The control study was performed in the same subjects who spend four days under dim light conditions (less than 200 lx). The subjects were allowed to sleep from 2400 to 0800 h. The onset phase, but not the end phase, of plasma melatonin rhythm was significantly phase-advanced by bright light exposure. Furthermore, the area under the curve of nocturnal melatonin rise was significantly larger under bright light exposure than under dim light. These findings indicate that midday exposure to bright light for 3 consecutive days changes the circadian organization of plasma melatonin rhythm in humans.

ENHANCED EXPRESSION OF PROTEIN KINASE C GENE CAUSED BY SOLAR RADIATION

Natural solar radiation (5 min of midday exposure in mid July, latitude 42 degrees N) induces protein kinase C mRNA almost two-fold in human epithelioid P3 cells in culture. This response is the same as that following tumor promotion by chemicals. The result indicates a possible role of promotion by solar UV radiation.

Photochemical Oxidants Potentiate Yield Losses in Snap Beans Attributable to Sulfur Dioxide

Field-grown snap beans (Phaseolus vulgaris) were given recurring midday exposures to sulfur dioxide in open-top field chambers containing ambient photochemical oxidants. There was a linear correlation (correlation coefficient = -.99) between increasing concentrations of sulfur dioxide and the yields of snap beans. Synergism was indicated for the mixtures of ambient ozone plus sulfur dioxide, leading to threefold greater yield losses in nonfiltered air than in charcoal-filtered air (to remove the ozone). Even the lowest sulfur dioxide dose in nonfiltered air reduced the yields of Astro, a cultivar that exhibited no visible pollutant-induced foliar injury.

Translocation Patterns in Soybeans Exposed to 14CO2 at Four Different Time Periods of the Day1

Field grown soybeans [Glydne max (L.) Merr.] were exposed at the mid.bloom stage to 14CO2 for 1 hour beginning at either 9 AM, 11 AM, 1 PM, or 3 PM CDT to evaluate the effects of time of day when exposed to 14CO2 on the translocation and distribution of labeled assimilates. Plants were harvested 0, 1, 3, 6, and 24 hours after labeling. By the end of the labeling period, 16.9% of the total recovered 14C had been exported from the leaves and 36.9% had been exported by the end of 24 hours (averaged over the four exposure times).Leaves labeled during the time periods associated with the highest net C fixation rates (11 to 12 AM and 3 to 4 PM) assimilated more 14C, translocated more to the stems and roots, and exhibited a higher rate of export from the leaves. Percent 14C recovered in each component (except nodules) was significantly different between the 9 to 10 AM and 3 to 4 PM exposure periods. Differences between the two midday exposures were relatively small, averaged over all harvest times and increased only when compared immediately and 24 hours after labeling.Carbon‐14 labeling and translocation experiments should be conducted during relatively constant time periods to allow nonconfounded intercomparisons between data when experimental technique dictates multiple times of exposure to 14C, especially between the early morning and late afternoon exposure periods.

Factors Controlling the Delimitation of Littoral Benthic Marine Algal Zonation

SYNOPSIS. The physiological and morphological responses of various littoral algal species to the stresses imposed upon the adults and sporelings by a number of interrelated factors in different latitudes are discussed in so far as there is experimental evidence that they delimit the vertical range of a species. The upper limits of algal zones in the eulittoral region are primarily determined by the resistance of the species to loss of water during midday exposure, by the effects of desiccation upon metabolism, by the ability to adjust their osmoregulatory processes during the periods of exposure to the rapid changes of salinity, and by the degree of tolerance to diurnal and seasonal changes of air temperatures. Low intensity of light reduces the metabolic efficiency and affects the resistance to desiccation and to variations in temperature and salinity. The lower limits of the eulittoral algal zones are primarily controlled by the intensity of light, by the competition with algae and invertebrates for space and light, and by grazing animals. The primary factors controlling the upper limits of the sublittoral algae are the depth of the wave base; the ability to utilize the submarine illumination as affected by turbidity and wave action in the layers of surface water; and the resistance to hydrostatic pressure. The lower limits of the sublittoral algae and both the upper and lower limits of theelittoral algal zones are controlled by the illumination and its effect upon the compensation-depth, the hydrostatic pressure, and the availability of nutrients.

Solar ultraviolet radiation in relation to sunburn and skin cancer.

This work is an exploration of some ways in which the physical characteristics of sunlight exert influence on the occurrence of sunburn and skin cancer. A summary of evidence relating skin cancer to radiation exposure includes published conclusions from Northern Hemisphere experience together with newer instances appearing in the Australian tropical population. A variety of evidence suggests that a study of skin cancer may be based on the assumption that the carcinogenic action spectrum is approximately the same as for sunburn independently of the fact that frequent sunburn accelerates the appearance of skin tumours. A very brief and somewhat speculative review is presented of biological aspects of skin cancer which are clearly related to radiation exposure. Variations in the relative effectiveness of sunlight have been calculated by combining the solar intensity spectrum at sea-level with the action spectrum for erythema (mild sunburn) of the skin. This is presented to show the influence of response spectrum, solar altitude, latitude, time of year and time of day.Methods of measurement are discussed by which an instrumental record may be obtained representing the erythemal or carcinogenic effectiveness of sunlight on human skin. Development and use of a fluorescent system is described in which magnesium tungstate phosphor is used to evaluate the different photon energies with a relative spectral responsiveness which is quantitatively similar to that for skin. Associated arrangements for measuring the resulting small currents are also included.Continuous records, covering several years, of the erythemal effectiveness of sunlight have been obtained by measurement at 7 sites ranging from 38°S latitude through 6°S in New Guinea to 53°N latitude. Condensed data from these records is presented in tables and diagrams which compare overall totals, monthly totals, average daily totals and maximum midday exposure rates for the observing sites, all of which have special features concerning the incidence of skin cancer. A variety of other environmental influences have also been investigated experimentally, the summarized findings being presented herein. These include day to day variations, cloudiness, skylight, shade, altitude, reflection and transmission by common substances.The overall total environmental effective exposure does net change as rapidly with latitude as is commonly believed. Nevertheless measurements from clear skies are in reasonable agreement with the relative calculated values at various latitudes and times of year. Attention is drawn to the way in which other aspects of exposure vary with latitude in a way which can be expected to have independent influence on the rate of development of skin cancer. These include the intensity during the day, the duration of potential sunburning levels, the continuity of exposure, recovery processes and personal habits.From the accumulated physical and biological factors which appear to contribute significantly towards human sunburn and skin cancer, recommendations are made giving a framework on which preventive measures may be based. These are considered in terms of environment, clothing, external screening devices and the application of sunscreens to the skin. While each of these involves a great amount of practical consideration, they are dealt with briefly here with the exception of the topical use of sunscreens. Since this has attracted considerable public attention, the logic and the uncertainties of the use of sunscreens has been examined in detail, much of which is presented here as the prophylactic approach in which the public appears to show the greatest interest. The information presented in this work throws more light on the environment in which skin cancer develops. While it does not prove directly any new factor as a cause of skin cancer, it does give strong support for some known factors and helps to reduce the significance of others. Opportunity is provided for epidemiologists to re-examine old data with direct reference to exposure levels. The physical evaluation also suggests new types of population data which could be informative. It also suggests important factors which may be ascertained from skin cancer patients, making clinical records of greater value as a probe on carcinogenesis. A logical approach to protective measures, apart from generally reducing skin cancer, may be used to study carcinogenesis in highly susceptible persons. Suggestions are made for the long-term continuation of improved physical measurement to monitor the environment against possible increases in the ultraviolet end of the terrestrial solar spectrum.

Carcinogenic effects of solar radiation and prevention measures.

It is well known that exposure to the sun is the major cause of cancer of the skin—the most common type of cancer encountered in this country. Little is known about the wavelengths responsible for this carcinogenic effect except that it is composed of the shortest wavelengths (290 to 320 mμ) of the solar spectrum. More quantitative information is available about wavelengths and energy requirements for induction of erythema by sun exposure. This may be pertinent to the cancer of the skin problem if it is assumed that erythema represents an early injury which ultimately develops into cancer of the skin. Protection of the individual's skin from sun exposure is the most effective preventive measure now available. This includes avoidance of intense mid-day exposure and use of topical sunscreen preparations when prolonged exposure is unavoidable. A protective effect has been demonstrated with some systemically administered agents but their use is not yet practical. Evidence that solar-induced erythema, degeneration and premalignant changes are reversible gives hope that more effective cancer preventive measures may become available for the patient with severe actinic damage.