How does ultraviolet light affect humans

Cataracts, an eye disorder characterized by a change in the structure of the crystalline lens that causes blurred vision, are a leading cause of blindness around the world - and excessive UV exposure is one of the risk factors in the development of cataracts.

In fact, persons who spend more time in the sun may develop cataracts earlier than others. The American Academy of Ophthalmology now recommends wearing UV sunglasses and a wide brimmed hat to lessen exposure to ultraviolet rays. Corneal sunburn, growths on the outer surface of the eye, retinal-tissue damage, and other eye diseases are also known, or suspected, to be related to long-term exposure to UV rays.

The skin is part of the body's natural defense system. Many healthcare professionals believe that UV radiation can alter immune system functions. When UV radiation suppresses immune responses, the body's ability to fight certain diseases, including skin cancer, is reduced. It is suspected that overexposure to UV radiation also interferes with the effectiveness of immunizations given through the skin. Studies have shown that sunscreens can prevent UV-induced wrinkling.

Animal studies demonstrated that sunscreens with adequate UVA coverage can prevent sagging and wrinkling due to high-intensity UVA. If you think you're at risk, make an appointment with one of our skin cancer experts at the Stanford Skin Cancer Program.

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Thank you for your patience. View the changes to our visitor policy » View information for Guest Services ». Finally, various research groups came to the conclusion that there was an unknown vitamin at work. This later became known as Vitamin D. Fish oil is one good source of Vitamin D, but it can also be generated in the skin, provided the skin receives enough energy from sunlight to do so.

There were two apparent solutions to the rickets problem then: adequate sunlight, and a diet providing sufficient Vitamin D. But urban areas were mostly dark and densely populated, with smog and smoke blocking the shortest waves of sunlight those most effective in battling disease. To really benefit from sunlight, people with rickets would need to leave the city or receive artificial sunlight therapy.

If a parent wanted their child to remain rickets-free but did not live in a sunny climate, the more practical option was to ingest fish oil instead. Now this lamp pours its rays into the system, your glands begin to work, and your food does you good again. Across the Atlantic, one of the most controversial proponents of light therapy was John Harvey Kellogg.

Famous for his breakfast cereal, Kellogg was also a doctor with a keen interest in nutrition, exercise and environmental treatments. He created a cabinet light bath to treat patients with a variety of ailments, including rheumatism, diabetes and anaemia.

Kellogg claimed that the artificial sunlight caused the skin to fill with blood and thus draw blood away from swollen areas and sick organs. By the s, a tanned complexion had come to be a desirable sign of health and well-being for many people in Europe and America. This was thanks, in part, to the dissemination of medical ideas about sunlight. If the weather was gloomy, or funds did not allow for a trip to warmer climes, sun worshippers could acquire a tan in the comfort of their home by means of a domestic sun lamp.

Many models were available and most promised users both health and beauty. Artificial sun lamps continue to be used today, but they reached peak popularity in Europe and America in the the s and s. Today, medical professionals warn that the UV rays emitted by sun beds can be dangerous.

Heliotherapy had firmly established the idea of the sun as a source of good health by the early s, but was not without naysayers. In , the New York Times ran an editorial lamenting the 'modern superstition that sunshine is always desirable':.

They do it under the queer delusion, for which there is no foundation of fact whatever, that thus they are getting back to nature and laying in a stock of health for future use. The truth is that they are taking rather desperate chances of wrecking what health they have and are storing up large quantities of future trouble [ Though the sun was seen by many as a source of wellbeing, it could still harm the body in a range of ways, from burning the skin to causing sunstroke or hurting the eyes.

This, of course, was nothing new. For centuries human beings have sought to shield themselves from the harmful effects of sunlight, devising protective attire and medicines to do so. Albarello drug jar for Billy goat's fat, Italy, — Animal fats were used as a common base for a number of ointments. Innuit snow goggles Some years ago in the Arctic regions of North America, Inuit people developed snow goggles, known as nigaugek or igguag, as a way to protect the wearer from snow blindness—a temporary loss of vision caused when the eye is overexposed to the ultraviolet rays of the sun.

Works photographic negative of man in pith helmet making cable joints, Madras In the late nineteenth century, British colonial forces adopted the pith helmet as part of their tropical uniform. Body cooling unit, London, Cooling beds such as this were originally designed to treat people affected by heatstroke during pilgrimages to Mecca in Saudi Arabia. The patient is sprayed with a mist of cool water and warmer air, causing rapid evaporation and cooling.

Swift treatment of heatstroke is vital to prevent permanent damage, coma or even death. Today, there is a recognised causal link between exposure to sunlight and the disease, but ultraviolet rays have long been suspected of having damaging effects. In , dermatologist Paul G. Unna linked skin cancer in sailors with exposure to ultraviolet light in his paper 'Carcinom der Seemanshaut'. Studies have found that people who use tanning beds or booths have a higher risk of skin cancer, including melanoma and squamous and basal cell skin cancers.

The risk of melanoma is higher if the person started indoor tanning before age 30 or 35, and the risk of basal and squamous cell skin cancer is higher if indoor tanning started before age In general, the American Cancer Society does not determine if something causes cancer that is, if it is a carcinogen , but we do look to other respected organizations for help with this.

Based on the available evidence, several expert agencies have evaluated the cancer-causing nature of UV radiation. One of its major goals is to identify causes of cancer. Based on the available data, IARC has made the following determinations:. The NTP has made the following determinations:. For more information on the classification systems used by these agencies, see Determining if Something Is a Carcinogen.

The FDA also requires that user instructions and sales materials directed at consumers including catalogs, specification sheets, descriptive brochures, and webpages carry the following statements:. The FDA has also proposed a new rule to ban the use of indoor tanning devices by anyone under age 18, to require tanning facilities to inform adult users about the health risks of indoor tanning, and to require a signed risk acknowledgment from all users.

Some US states have already banned indoor tanning by all people younger than 18, while others have banned use by younger teens and children. In addition to skin cancer , exposure to UV rays can cause other health problems:. Some people are more sensitive to the damaging effects of UV radiation. Some medications can also make you more sensitive to UV radiation, making you more likely to get sunburned.