Ultraviolet-B

Ultraviolet-B is electromagnetic radiation with wavelengths of about 280–315 nanometers. Stratospheric ozone absorbs much of it, but some reaches Earth’s surface.

Ultraviolet radiation: Electromagnetic radiation with wavelengths shorter than visible light and longer than X-rays. Ultraviolet-B is one band within this broader region of the electromagnetic spectrum.
Vitamin D: A group of fat-soluble compounds that regulate calcium and phosphate balance in the body. Ultraviolet-B initiates vitamin D production in skin by converting 7-dehydrocholesterol.
Sunburn: An inflammatory skin reaction caused by excessive exposure to ultraviolet radiation. Ultraviolet-B is a major cause of sunburn after intense solar exposure.
Ultraviolet-A: Ultraviolet radiation with wavelengths of about 315–400 nanometers. Ultraviolet-A has longer wavelengths and is less strongly absorbed by ozone than ultraviolet-B.
Ozone layer: A region of the stratosphere with elevated ozone concentrations that absorbs much incoming ultraviolet radiation. Ozone absorption removes much, but not all, incoming ultraviolet-B before it reaches the ground.
Phototherapy: Medical treatment that uses controlled exposure to light or other electromagnetic radiation. Narrowband ultraviolet-B is a common phototherapy treatment for inflammatory skin diseases.
Skin cancer: A group of cancers arising from abnormal growth of cells in the skin. Repeated ultraviolet-B damage contributes to mutations associated with several skin cancers.
Visible spectrum: The range of electromagnetic wavelengths detectable by the human eye, roughly 380–700 nanometers. Ultraviolet-B lies beyond the short-wavelength edge of visible light and cannot be seen unaided.
DNA photodamage: Molecular damage to DNA caused when absorbed radiation alters its chemical structure. Ultraviolet-B can directly damage DNA, producing lesions that disrupt replication and transcription.
Psoriasis: A chronic immune-mediated disease that causes inflamed, scaly patches on the skin. Controlled ultraviolet-B exposure can slow excessive skin-cell growth and reduce psoriasis symptoms.

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