Dear Ms McDaniel,

Thanks for the information on protecting skin from sunburn. I'm not using any sun protection because I had an allergic reaction when I used a particular brand of sunblock as well as some popular brands of lip balms. My face got some pimples and my lips became swollen. As a result of those experiences, I'm not sure which brand to buy since I think that they all have the same key ingredients. Is there anything you could suggest? I would greatly appreciate it as I really need to protect my skin.

Dear Reader,

I understand how you feel, since applying sunblock to the skin before exposure to sunlight is responsible behaviour. However, this appears to be backfiring. I think the allergic reaction you reported could be contact dermatitis, an itchy sort of skin rash which some people, especially teenagers and the middle-aged, get when they apply substances like cosmetics. Remember that many cosmetics contain sunscreens.

Photo-contact dermatitis occurs when the itchy rash appears on the face, ears, lower neck and upper chest, areas which are most exposed to the sun. A negative reaction to sunscreen may occur if you have an allergy to the active ingredients in the product or sometimes if you are allergic to the inactive ingredients in the product, like preservatives and perfumes.

One method of determining if you have contact dermatitis is to perform a patch test. A dermatologist is the ideal professional for this job. The ingredient has to be applied to a small area, in a particular concentration (usually five per cent or 10 per cent strength) in a specific vehicle like petrolatum.The dermatologist may want to rule out other possible causes for your skin reaction to sunscreen - conditions like lupus and porphyrias.

The usual suspects

The chemicals in sunscreens which are usually responsible for contact dermatitis and photo-contact dermatitis reactions include para-aminobenzoic acid (PABA). Many people have reported skin sensitivity to PABA. The good news is that most sunscreens have now excluded PABA from their list of ingredients. Benzo-phenones are involved in most sunscreen-induced contact dermatitis. The aliases include oxybenzone, methanone, diphenyl-ketone or benzophenone-3.

Cinnamates do not dissolve well, so they are usually found in sunscreens marked 'water-proof'. You find them combined with the benzo-phenones described above. Their names usually end in 'cinnamate' and the main cinnamate in sunscreens is also known as Parsol MCX.

Dibenzoylmethanes are sunscreens, like avobenzone (also called Parsol 1789) and another product known as Eusolex 8020.

Plan of Action

Identification of the ingredient(s) to which you are allergic, may be the most difficult task. The brand of sunscreen to which you are allergic contains avobenzone. You may want to try the physical sunblocking agents, titanium dioxide and zinc oxide.

Interestingly, this brand also has a formulation called 'sensitive skin', which does not contain the avobenzone, but contains titanium dioxide and zinc oxide, two ingredients which have not been reported to cause contact dermatitis or photo-allergy.

Dahlia McDaniel is a pharmacist and final-year doctoral candidate in public health at the University of London; email: yourhealth@gleanerjm.com.