White : Diseases of the Skin - Photodermatology and Photodermatoses

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Gary M. White & Neil H. Cox

Diseases of the Skin

17	Photodermatology and Photodermotosess

SUN PROTECTION

Sun avoidance and clothing

Physical avoidance of sunlight is important in everybody, but is of critical importance in treatment of patients with photodermatoses. Patients should be advised:

•	to avoid sunlight, especially between 10 a.m. and 4 p.m.;
•	to sit in shade;
•	to wear protective clothing, such as long-sleeved shirts with a close weave and wide-brimmed hats;
	to be aware that many photodermatoses are UVA-triggered and may therefore be provoked even on dull days, and that UVA tanning beds are contraindicated;
	to use sunscreens (see later); and
	in severe cases, to consider UVA-blocking adhesive film on house and vehicle windows.

Sunscreens

Therapeutically relevant points regarding sunscreens that may influence choice, or that may need to be explained to patients, include the following.

•	Chemicals used in sunscreens may be divided into absorbent and reflective types (many modern sunscreens contain a mixture of both).
•	Most of the absorbing chemicals block UVB wavelengths well, but UVA wavelengths poorly, although the benzones block UVA. Reflective agents will give protection more broadly across the spectrum. This is important, as most photodermatoses are triggered by UVA.
•	Sun protection factor (SPF) ratios refer to the UVB sunburn-blocking activity of the sunscreen; however high the quoted UVB SPF, UVA can generally be blocked only about eightfold, even with reflective-type sunscreens.
	The SPF achieved depends on the thickness of application; most people apply less than the amount used by manufacturers when determining the SPF.
	For most photodermatoses, a reflective sunscreen (usually titanium dioxide), or one containing a combination of high-potency UVA- and UVB-absorbing chemicals, is required.
	Most commercial sunscreens contain fragrances and often other potential sensitizers (especially hydroxybenzoates), which it may be important to avoid.
	Patients who are allergic to sunscreens need to be aware that these are often incorporated into cosmetics, emollients, lip salves, and antiaging creams.
	Artificial tanning agents do not in themselves give any UV protection; some contain added sunscreen but usually at low SPF, so patients with light sensitivity should also use a reliable sunscreen.

PRACTICE POINTS

•	Sunscreens are much better at blocking the burning effects of UVB than they are at blocking UVA, which is more important for aging changes and for provocation of many photodermatoses.
•	In patients with photosensitivity, especially chronic photosensitivity dermatitis, who continue to have problems despite use of an appropriate sunscreen, it is important to consider sunscreen allergy or photocontact allergy.
•	Artificial tanning agents do not block UV radiation, and thus do not prevent sunburn.
	Physical protection from sunlight by avoidance or using suitable clothing gives much better protection than any sunscreen can achieve.
	For most photodermatoses, a reflective sunscreen (usually titanium dioxide), or one containing a combination of high-potency UVA- and UVB-absorbing chemicals, is required.
	Most commercial sunscreens contain fragrances and often other potential sensitizers (especially hydroxybenzoates), which it may be important to avoid.
	Patients who are allergic to sunscreens need to be aware that these are often incorporated into cosmetics, emollients, lip salves, and antiaging creams.
	Artificial tanning agents do not in themselves give any UV protection; some contain added sunscreen but usually at low SPF, so patients with light sensitivity should also use a reliable sunscreen.

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