UV radiation can affect human health, both positively and negatively. First, the beneficial effects are as follows;

• Helps in producing Vitamin D in Human Skin: Its main positive effect is related to Vitamin D production in human skin, which is catalyzed by UVB light. Vitamin D has a significant role in bone health and the prevention of osteoporosis and osteomalacia. Additionally, it affects a variety of adult health problems. It lowers blood pressure in hypertensive patients; the incidence and severity of cardiovascular disorders, type 2 diabetes, and rheumatoid arthritis, and also helps in preventing tooth loss.
  
  Vitamin D also has a significant role in reducing mortality from various cancers, including colon, breast, prostate, ovarian, and even - ironically - melanoma (the most severe form of skin cancer). 
  
  For most children and adults, the major source of vitamin D is which obviously creates a public health dilemma since UV radiation also causes skin cancers. Studies were conducted to determine whether the amount of vitamin D made from everyday exposure to sunlight is sufficient to acquire an optimum vitamin D blood level. The results are controversial; some studies show that even with sunscreens, a proper amount of vitamin D can be produced in the skin, while other studies show that many people have insufficient levels for most of the year, especially during and after winter.
   
• Helps in certain skin conditions: Exposure to UV radiation in the form of lasers, lamps, or a combination of these devices is helpful in certain skin conditions that do not respond to other methods of therapy. Such skin conditions include psoriasis (extreme skin dryness), eczema, certain fungal skin infections, and acne, among others. 
  
  Phototherapy involves exposing a patient to a carefully monitored dose of UV radiation on a regular schedule. this type of therapy does not eliminate the negative side effects of UV exposure, however, treatment is carefully supervised by a healthcare professional to ensure that the benefits outweigh the risks.
   
• Helps in reducing depression: Sun exposure has also been found helpful to reduce the severity of depression in patients with seasonal affective disorders.

Exposure to UV radiation, whether outdoor or indoor, also carries a potential risk to human health, which is listed as follows;

• Tanning: Tanning is not healthy, and is a sign of skin damage. This damage builds up and accelerates aging and can also increase the risk for all types of skin cancer. Both the US Department of Health and Human Services and WHO have identified UV as a proven human carcinogen. 
  
  UV radiation is considered the main cause of non-melanoma skin cancers, including basal cell carcinoma and squamous cell carcinoma. Additionally, UV radiation is one of the major risks for the development of melanoma, the deadliest form of skin cancer, especially for fair-skinned people.
  
  Skin cancer is the most common of all cancers in the US. According to current statistics, more than 3.5 million non-melanoma skin cancers in more than 2 million people are diagnosed in the US annually. On a molecular level, exposure to UV radiation can result in DNA damage, leading to the formation of malignant cells as well as immunosuppression.
   
• Eye Diseases: UV radiation is also linked with various eye diseases, including cataract formation and retinal degeneration.
   
• Aging: UV radiation plays a leading role in photoaging and the premature appearance of lines and wrinkles as well as sun spots.
   
• Melanocytes: UV radiation causes the melanocytes, located in the basal cell layer of the epidermis, to produce melanin, which is the pigment that makes the skin darker.

It is important to understand the relationship between skin pigmentation and photoprotection from the perspective of skin cancer. Studies show that melanin provides the skin with natural protection against solar damage by serving as a physical barrier and an absorbent.

However, the amount of melanin that is produced in fair-skinned people following exposure to the sun is relatively low and does not afford them adequate protection. Therefore, they must take additional precautions to prevent solar skin damage. The efficacy of melanin as sunscreen is assumed to be SPF 1.5 to 2.0, maximum SPF of 4, meaning that melanin absorbs 50-75% of UV radiation.

Dark skin, which contains more melanin than fair skin, is better protected against UV - induced damage. That is why dark-skinned people often look younger than fair-skinned people of the same age. Nevertheless, even dark-skinned people should avoid excessive sun exposure. While the epidermis of African American skin allows only 7.4% of UVB and 17.5% of UVA to penetrate, 24% of UVB and 55% of UVA pass through Caucasian skin.

Claims made about the healthfulness of indoor tanning are misleading since they may make consumers believe that they can acquire effective protection when tanning. The amount of melanin produced, however, is not enough to be an effective filter against UV radiation. It should also be kept in mind that all types of UV-induced tanning, either outdoor or indoor result in DNA damage and cellular damage and can lead to photocarcinogenesis (i.e., cancer formation).

Interesting Facts
Studies have shown that UVA oxidizes the existing melanin, causing immediate pigment darkening. UVB causes inflammation, which releases new melanin and in about 72h, leads to further taking that lasts much longer than UVA-triggered tanning. All of this melanin production signals that DNA damage has already occurred; it is the body's imperfect attempt to protect the skin from further damage. Nonetheless, the damage from repeated UV exposures keeps accumulating and can ultimately lead to skin cancer.