allergic to the sun??

I have always had a problem with herpes being triggered by the sun.  I have always used the chapstick spf 30 with no problem
and also have a perscription for zovirax cream and famciclovir pills.

This summer however, when I go out in the sun, with sunscreen, hat, trying to stay in shade etc.  Its almost like an allergic reaction only on my lips....they get very red and swollen, and very itchy, and feel like they are burned even with all the sunscreen. and a very small blister will appear below the bottom lip, not on it, like the herpes blister.  I take an antihistamine, and put different ointments on, (allergy cream makes them sting )  and it goes away in about 3 days...until I go out in the sun again.  My physician is puzzled and says my lips definitley look like an allergic reaction ......my question is....what can I put on them to BLOCK the sun completely??  Ive tried Plain old fashioned Zinc Oxide, which worked better than everything else...the reaction was less severe..but there still was one....But was wondering if there was an invisible block out there to use - and also, have you ever come across this type of reaction before?  I live near the Ocean....going out in the sun is part of life......

THanks for any info you can give

[Dr_Aparna]

Hi,
Cholinergic urticaria is a subcategory of physical urticaria (aka hives) that is a skin rash brought on by a hypersensitive reaction to body heat. Symptoms follow any stimulus to sweat such as exercise (sometimes called exercise-induced urticaria), heat from the sun (which could also indicate solar urticaria), saunas, hot showers (reaction to water can also indicate water urticaria), spicy foods which may cause an increase in body temperature or even stress due to blushing or anger.

All urticarias are caused by an elevated histamine release by the body's mast cells. With cholinergic urticaria the exact triggering mechanism for this response is unknown, but it is assumed to be related to the body's thermoregulatory response.

Drug treatment is typically in the form of antihistamines such as loratadine (Claritin), hydroxyzine, cetirizine.

Diet changes are often tried by people with urticaria in attempts to stop what is presumed to be a food allergy. Also, people often try changing their laundry detergents, shampoos, soaps, etc. While food and other allergies can cause hive outbreaks, cholinergic urticaria and other urticaria outbreaks often occur on their own with no connection to food or other allergy.
ref:http://en.wikipedia.org/wiki/Cholinergic_urticaria
In your case the best thing to do is to avoid exposure as much as you can and if you have to then do the best that you can with the sunscreen/sunblocks that are available.