Excessive Sunlight Exposure
Exposure to sunlight, in moderate amounts, is enjoyable to most people, as well as having certain health benefits.1 For example, direct exposure of the skin (i.e., hands, face, arms, etc.) to sunlight leads to the formation of vitamin D. Adequate amounts of vitamin D in the body prevent rickets and osteomalacia (the deficiency diseases of vitamin D) and reduce the risk of osteoporosis. Seasonal differences in deaths from heart disease have been suggested by some researchers to be partly related to reduced exposure to sunlight in the winter months.2 Ultraviolet light (from sunlight and other sources) has been used to treat psoriasis and some other skin conditions.3 Sunlight has also been linked to reduced risks of prostate,4 colon,5 ovarian,6 and breast cancers.7 The anticancer effect is thought to result from synthesis of vitamin D resulting from exposure to sunlight. Excessive sunlight, however, particularly sunburn, can be detrimental to health in many ways.
(The following list is comprehensive, although not necessarily exhaustive. Contact your healthcare professional for more information.)
Skin aging is a process of changes in the structure and elasticity of the skin over time. It may be a normal part of aging or it may be due to the effects of ultraviolet radiation, usually through exposure to sunlight. Increased exposure to sunlight directly increases skin wrinkling and aging.8
Skin cancers include squamous cell and basal cell carcinomas. Both are very common, but generally curable with conventional treatment. Excessive exposure to sunlight has been linked to both.9 Excessive exposure to sunlight is also strongly linked to malignant melanoma, the most life threatening but least common form of skin cancer.10
Cataracts develop when damage to the protein of the lens of the eye clouds the lens and impairs vision. Cataracts are more likely to occur in those who are exposed to excessive sunlight, which leads to oxidative damage. Oxidative damage to the lens of the eye appears to cause cataracts in animals11 and people.12 Sunglasses are believed to reduce this risk.
The macula is a portion of the retina in the back of the eye. Degeneration of the macula is the leading cause of blindness in elderly Americans.13 Sunlight triggers oxidative damage in the eye, which in turn is believed to contribute to macular degeneration.14 In theory, sunglasses should reduce this risk.
Several conditions, such as erythropoietic protoporphyria and polymorphous light eruption, share the common symptom of hypersensitivity to light—typically sunlight. People with photosensitivities need to protect themselves from the sun by using sunscreen, wearing protective clothing (such as long-sleeved shirts), and avoiding excess exposure to the sun. People taking certain prescription drugs (sulfonamides, tetracycline, and thiazide diuretics) and those diagnosed with systemic lupus erythematosus are more likely to overreact to sun exposure.15,16 The herb St. John’s wort could, theoretically, make the skin more sensitive to sunlight, but this is rare when used at recommended levels.17 However, fair-skinned individuals should be alert for any rashes or burns following exposure to the sun.
1. Ness AR, Frankel SJ, Gunnell, Smith GD. Are we really dying for a tan? BMJ 1999;319:114–6.
2. Grimes DS, Hindle E, Dyer T. Sunlight, cholesterol and coronary heart disease. Q J Med 1996;89:579–89.
3. Ness AR, Frankel SJ, Gunnell, Smith GD. Are we really dying for a tan? BMJ 1999;319:114–6.
4. Hanchette CL, Schwartz GG. Geographic patterns of prostate cancer mortality. Evidence for a protective effect of ultraviolet radiation. Cancer 1992;70:2861–9.
5. Ainsleigh HG. Beneficial effects of sun exposure on cancer mortality. Prev Med 1993;22:132–40.
6. Lefkowitz ES, Garland CF. Sunlight, vitamin D, and ovarian cancer mortality rates in US women. Int J Epidemiol 1994;23:1133–6.
7. Ainsleigh HG. Beneficial effects of sun exposure on cancer mortality. Prev Med 1993;22:132–40.
8. Fisher GJ, Wang ZQ, Datta SC, et al. Pathophysiology of premature skin aging induced by ultraviolet light. N Engl J Med 1997;337:1419–28.
9. Whittaker S. Sun and skin cancer. Br J Hosp Med 1996;56:515–8.
10. Melia J. Skin cancer. Health Hyg 1995;16:153–8.
11. Schocket SS, Esterson J, Bradford B, et al. induction of cataracts in mice by exposure to oxygen. Isr J Med Sci 1972;8:1596–601.
12. Palmquist B, Phillipson B, Barr P. Nuclear cataract and myopia during hyperbaric oxygen therapy. Br J Ophthalmol 1984;68: 113–7.
13. National Advisory Eye Council. Report of the Retinal and Choroidal Diseases Panel: Vision Research CA National Plan: 1983–1987. Bethesda, MD: US Dept of Health and Human Services, 1984. National Institutes of Health publication 83–2471.
14. Young RW. Solar radiation and age-related macular degeneration. Surv Ophthalmol 1988:32:252–69.
15. Vassileva SG, Mateev G, Parish LC. Antimicrobial photosensitive reactions. Arch Intern Med 1998;158:1993–2000.
16. Wananukul S, Watana D, Pongprasit P. Cutaneous manifestations of childhood systemic lupus erythematosus. Pediatr Dermatol 1998;15:342–6.
17. Brockmöller J, Reum T, Bauer S, et al. Hypericin and pseudohypericin: Pharmacokinetics and effects on photosensitivity in humans. Pharmacopsychiatry 1997;30(suppl):94–101.