Red rash over body recurring multiple times in 2 weeks

Patient: Over the past 2 weeks I have had what appears to be an allergic reaction to “something”. It starts on my face, becoming red and swollen – like a bad sunburn, then progresses to my arms, torso and lower legs. We are currently thinking it might have to do with my new/used car and possibly new clothing. It seems to be systemic as opposed to a “contact dermatitis” because it spreads and does not seem to be confined to an area touching something. It has occurred 4 x in the past 2 weeks. Each time I was in or had just left my car. 2x I was wearing a new shirt (different shirts) that had not yet been washed. Each time I took benadryl, 1x I took a shower and one time I applied cool compress. It does not seem “need” to be washed off. any thoughts… it seems pointless to make an appt to go to the doctor for this (will ask at next check up) because it goes away quickly with meds. Thoughts?

Symptoms: Red rash over most of body – responds to benadryl.

Doctor: Thank you for your question. This systemic rash seems to be a reaction to an allergen within your car. This could possib ly be due to an allergen within your vehicle. Often dust and debris can build up within you vehicle and its ventilation system, which you can be exposed to resulting in a systemic allergic reaction. We are lead to believe that this is more of an allergy versus another etiology because you asserted that this responds well to the use of antihistamines – benadryl (diphenhydramine). You are correct in asserting that contact dermatitis has more of a localized appearance however, you may have a very strong sensitivity to a particular allergen in which a larger surface of your body responds. In order to determine what the exact allergen is that is affecting you, we recommend that you consult a specialist in Allergy and Immunology who will conduct allergy testing. Once you are allergy is determined, you can take measures to prevent your exposure to said allergen. In the meantime, it would be recommend to have the interior of your vehicle thoroughly cleaned and vacuumed, vacuuming of the ventilation ducts, and change the cabin air filter of your vehicle.Thank you for consulting