Environmental radon (222Rn) is ubiquitous with a World Health Organization estimated mean global indoor radon concentration of 39 Bq/m3. Contrary to the common belief, we show that radon indeed accumulates in the human body and, hence, is not in passive equilibrium with environmental radon. Further, although a noble gas, radon reacts by forming van der Waals bonds. Moreover, radon is lipid soluble, its solubility in fatty acids (FA) dependent upon the number of carbon atoms, reaching a maximum, in the region of heptanoic acid, of 7.4 times that of ambient air concentration. Paradoxically, radon solubility varies inversely with temperature. Radon moves freely into the brain where it decays to one of its numerous progeny. Each resulting metal remains firmly bound to the underlying brain structure; 222Rn progeny, 210Bi, a beta emitter, and 210Po, an alpha particle emitter, accrue selectively in the brain in PD. The human brain is exceptionally rich in lipids (which are made up of FA), serving as structural components in cell membranes. Reduced polyunsaturated fat (PUFA) levels have been reported in the substantia nigra in PD compared to other brain regions and control tissue. We hypothesize that brain tissue in PD exhibits an imbalance in the ratio of saturated fatty acids (SFA) to PUFA. Radon accumulates in PD brain tissue because SFA are denser in carbon, thereby allowing 210Bi and 210Po progeny to accumulate. (All studies from which human data are reported were approved by the University of North Dakota Institutional Review Board and were conducted according to the Basic Principles of the Declaration of Helsinki.)