UVB

UVB refers to ultraviolet radiation with wavelengths roughly between 280 and 315 nanometers. It is a portion of the solar spectrum that reaches the Earth's surface, though its intensity varies with latitude, season, time of day, altitude, and atmospheric conditions. UVB is also emitted by some artificial sources, including certain tanning lamps and phototherapy devices.

Biological effects of UVB are significant. It is energetic enough to cause sunburn and DNA damage in skin cells, predominantly through the formation of cyclobutane pyrimidine dimers and other photoproducts. The skin has repair mechanisms, but excessive exposure increases the risk of skin cancer and photoaging. UVB also drives the skin’s production of vitamin D3 by converting 7-dehydrocholesterol to previtamin D3, which is then metabolized to the active hormone vitamin D.

Health implications and protection. Adequate UVB exposure is important for maintaining vitamin D status, which supports bone health and may have other physiological roles. However, excessive exposure raises the risk of erythema, DNA damage, and skin cancer. The ozone layer absorbs a substantial portion of UVB, but surface exposure still varies with sun angle and environmental conditions. Protective measures include broad-spectrum sunscreen with UVB filters, protective clothing, hats, and shade. Individual needs depend on skin type and geographic factors.

Medical use and safety. UVB phototherapy, particularly narrowband UVB around 311–313 nm, is used to treat conditions such as psoriasis, atopic dermatitis, and vitiligo under medical supervision. Potential side effects include skin redness, dryness, and long-term concerns with high cumulative exposure.