L4 EFFECTS OF UV RADIATION ON HAIR
Camacho FM
Department of Medical-Surgical Dermatology and Venereology, Hospital Universitario Virgen Macarena, Sevilla, Spain

The ultraviolet radiation determines different pathological situations when it acts on the scalp. One of them is in relation with the gradual reduction of hair and its possibility to damage the scalp more easily. The others are a direct consequence of the action of UVR on hair follicles.
a) Pathological conditions as a consequence of the action of UVR on unprotected scalp:
• Photosensitive disorders: Cicatricial alopecia in chronic discoid lupus erythematosus and porphyries. Acute alopecia in photosensitive eczema
• Disorders of the photodamaged scalp: Solar elastosis, rosacea, actinic keratosis (KIN).
b) Direct effects of UVR on hair follicles:
• Androgenetic alopecia:
AGA is a photoaggravated alopecia.
Follicular microinflammation:
- The role of porphyrins produced by Propionibacterium acnes.
- The role of interleukin 1a and radical oxygen species produced by keratinocytes.
- The role of fibroblasts in response to proinflammatory signals.
• Telogen alopecia:
Telogen effluvium after long sun exposure, at least six hours. It usually appears 3-4 months after the sunburn. Described in 17 men treated with 0.01% tretinoin for androgenetic alopecia and 5 women with hairstyles that permits direct exposure to UVR of several areas of scalp. Trichograms with high proportion of telogen and dystrophic hairs could be seen. Men show an increase of frontovertical hair shedding and women present a loss of the frontal hair implantation line with unruly hairs on the frontal area. The role of the columns of cells in the hair shafts acting as fiberoptic system may be considered as the pathogenic mechanism. Tretinoin was removed of treatment for MAGA and we never saw more this type of alopecia in men, but we now see telogen alopecia after sunburn in women and men with the current hairstyles.
All types of alopecia need photoprotection to avoid the production of reactive oxygen species (ROS). Antioxidant supplements, such as carotenoids (provitamin A), ascorbic acid (vitamin C) and D-a-tocopherol (vitamin E) can help to boot cellular antioxidant mechanisms and alleviate the damage wrought by oxidative stress:
• Increase of lutein concentrations in the skin decreases the content of ROS after UVR exposure.
• Intake of vitamin C and E reduces the sunburn reaction to UVB irradiation.
• Physical photoprotection using broad-brimmed hats is convenient.
• The role of Polypodium leucotomos protecting against long-term UV-induced skin damage must be more investigated.