Bright red and stinging! how to tell if i had an allergic reaction and can i use vaseline to soothe it?

Vaseline is safe: Allergic reactions manifesting as skin rash can be red, itchy, burning, stinging, raised, blister-like or flat, limited or widespread. Itching is a very common symptom. Sometimes it is hard to tell, but a person should try to recall using a new soap, detergent, lotion, hair care product, or other medication or agent was applied to the skin. Also ingested medications or foods could trigger rash.