UVB Radiation: Effects, Risks and Protection

What is UVB Radiation?

UVB radiation (ultraviolet B radiation) is a segment of the electromagnetic spectrum of solar radiation with wavelengths ranging from 280 to 315 nanometers (nm). It falls between the shorter-wavelength UVC radiation (below 280 nm) and the longer-wavelength UVA radiation (315–400 nm). Although UVB accounts for only a small fraction of the UV radiation reaching the Earth's surface – most is absorbed by the ozone layer – it has significant biological effects on the human body.

Biological Effects on the Skin

UVB radiation primarily penetrates the outermost layer of the skin (epidermis), triggering a range of biological processes. These effects can be both beneficial and harmful.

Positive Effects

• Vitamin D synthesis: UVB radiation stimulates the conversion of 7-dehydrocholesterol into previtamin D3 in skin cells, which is subsequently converted to vitamin D3 (cholecalciferol). This is the primary natural pathway for vitamin D production in the human body.
• Mood enhancement: Sunlight, including UVB, may promote the release of serotonin, contributing to improved mood and well-being.
• Therapeutic use: Controlled UVB exposure is used medically to treat skin conditions such as psoriasis, vitiligo, and atopic dermatitis.

Negative Effects

• Sunburn: Intense UVB exposure causes erythema (skin redness) and sunburn due to DNA damage in skin cells.
• DNA damage: UVB radiation can directly damage the DNA in skin cells, particularly through the formation of pyrimidine dimers, which can lead to mutations over time.
• Premature skin aging: Repeated UVB exposure accelerates the breakdown of collagen and elastin in the skin.
• Skin cancer: Chronic UVB exposure is considered a primary risk factor for non-melanoma skin cancers (basal cell carcinoma, squamous cell carcinoma) and malignant melanoma.

Factors Influencing UVB Intensity

The intensity of UVB radiation reaching the Earth's surface depends on several factors:

• Time of day: UVB intensity is highest between 10 a.m. and 4 p.m.
• Season: UVB levels are significantly higher in summer than in winter.
• Geographic location: UVB exposure is greater near the equator and at high altitudes.
• Ozone layer: Depletion of the ozone layer leads to increased UVB levels at the surface.
• Cloud cover and reflection: Clouds can partially reduce UVB; snow, water, and sand reflect UVB and amplify exposure.

UV Index and Sun Protection Recommendations

The UV Index (UVI) is an internationally standardized measure of UV radiation intensity. The higher the UV Index, the greater the risk of skin damage. Health authorities such as the WHO recommend protective measures when the UV Index reaches 3 or above:

• Apply sunscreen with a sufficient sun protection factor (SPF)
• Wear protective clothing, hats, and sunglasses
• Seek shade during midday hours
• Avoid tanning beds and sunlamps

Medical Use of UVB Radiation

In dermatology, UVB radiation is used therapeutically under controlled conditions. Narrowband UVB therapy (NB-UVB) at a wavelength of approximately 311 nm is considered particularly effective and well-tolerated for treating:

• Psoriasis
• Vitiligo
• Atopic dermatitis (eczema)
• Cutaneous T-cell lymphoma

The therapy is administered under medical supervision in controlled doses to minimize the risk of DNA damage.

UVB Radiation and Vitamin D Deficiency

In regions with limited sunlight – especially during winter months at northern latitudes – insufficient UVB exposure can lead to vitamin D deficiency. This is particularly relevant for older adults, individuals with darker skin tones, and people who spend little time outdoors. In such cases, vitamin D supplementation may be recommended.

References

1. World Health Organization (WHO) – Ultraviolet radiation and health. Available at: https://www.who.int/news-room/fact-sheets/detail/ultraviolet-radiation
2. Lucas R. et al. – Solar ultraviolet radiation: Global burden of disease from solar ultraviolet radiation. World Health Organization, Environmental Burden of Disease Series No. 13, 2006.
3. Holick M.F. – Vitamin D Deficiency. New England Journal of Medicine, 357(3):266–281, 2007.