Another allergy event

Today during my 8yo's dance class I took my 3yo old to my sisters. She just ran around and played. We were only there about 30 minutes and when we went to leave she started itching like crazy on her hands and face. She hadn't eaten anything, but she had red welts around her mouth and on her hands. We left to pick up her sister and in the car she was going crazy itching. We got to dance and went to the bathroom, rinsed her hands and face and I gave her a wet towel to hold on any parts that itched. Within 20 minutes, the welts went away and she was no longer itchy. Just another unknown allergy episode to add to the list. Lord help us! We cry MRSA-y!