Table of Content


Autumn 2007, Vol. 15 No. 3

Hong Kong J. Dermatol. Venereol. (2007) 15, 118-127

Review Article

Factors affecting the clinical efficacy of sunscreens

TTY Ho 何天儀

The efficacy of a sunscreen to protect the skin against the various detrimental effects of ultraviolet radiation (UV) depends on (1) its protection spectrum; (2) photostability of the product; and (3) how it is applied. Ideally, a sunscreen should provide adequate protection (depth) across the whole of the UV spectrum (breadth), including UVAI. Labelling of UVA protection is not universal and different definitions are used with the Persistent Pigment Darkening (PPD) method being the most popular. Photoinstability is a factor which may affect the efficacy of sunscreens especially in the UVA range. Newer UVA filters are now available which are photostable. Sunscreens should be applied at a thickness of 2 mg/cm2 to achieve the stated protection. Unfortunately, sunscreens are often applied at much lesser amounts resulting in drastic reduction of the level of protection.