Topical sunscreens are made up of constituents that either absorb or reflect incident radiation. Absorbents are organic chemicals such as para-aminobenzoic acid (PABA) and its derivatives, cinnamates, bezophenones and salicylates. None of these offer significant protection against UVA radiation. Exceptions are dibenzoylmethane derivatives and anthranilates which offer mild UVA protection whilst still acting to absorb radiation (1,2).
Reflectants are generally inorganic compounds such as zinc oxide and titanium dioxide (1,2,3). These offer significant UVA and UVB protection. However, they are cosmetically less acceptable due to their tendency to leave a visible white film.
A full list of prescribable sunscreens is listed in section 13.8.1 of the BNF.
Notes:
- Sun Protection Factor (SPF) is the most important data to quantify the effectiveness of a sunscreen, being universally accepted
- amount of protection offered against ultraviolet B (UVB) radiation is indicated by the sun protection factor (SPF) of the preparation
- the method of calculating the SPF of a sunscreen is based on determining the minimum erythematous dose (MED), defined as the smallest amount of energy required for triggering the erythema, in areas of protected and unprotected skin. The SPF value is then calculated as the ratio between the MED of protected and unprotected skin
- quantifies the protection that a product is able to offer in terms of exposure time in relation to sunburn when compared to unprotected exposure
- therefore, if a particular sunscreen has SPF 30, this means in practice that a sun exposure 30 times greater is necessary to produce erythema, compared to the situation in which this user would not be photoprotected
- When selecting a sunscreen there are two important things you should check when buying sunscreens (4):
- The sun protection factor the higher the factor the greater the protection provided against the burning rays of the sun (ultraviolet B)
- The star rating the more stars there are the better the level of protection against the aging rays of the sun (ultraviolet A). The maximum protection available is five stars.
Reference:
- Norris, P.G. & Ratnavel, R.C. Sunscreens and their medical uses', Prescribers' Journal 1993;33(2): 63-71.
- McGregor JM, Young AR. Sunscreens, suntans, and skin cancer. BMJ 1996;312: 1621.
- Diffey BL. Sunscreen and melanoma: The future looks bright. Br J Dermatol. 2005;153:378-81.
- Salford Royal NHS Foundation Trust (Accessed 8/6/14). Sunscreen.