Latex allergy allergy is an IgE (immune) mediated reaction to proteins found in the "Hevea brasiliensis" tree, a type of rubber tree. Testing for type I natural rubber latex allergy is through blood testing to determine if the patient is producing IgE antibodies to latex proteins. Anaphylactic shock can be provoked in allergic persons by the "previous" use of latex in an area: latex is typically powdered to prevent sticking, latex proteins become attached to the particles of powder, and the powder becomes airborne when the latex item is used, triggering potentially life-threatening Type I reactions when the latex-contaminated powder is inhaled
Allergic contact dermatitis the eyelids, say from use of makeup, touching the contact allergen with the fingers can trigger an allergic reaction on the eyelids. This is due to local skin memory T-cells, which remain in the original sensitization site. In a similar fashion, cytotoxic T lymphocytes patrol an area of skin and play an important role in controlling both the reactivation of viruses (such as the "cold sore" virus) and in limiting its replication when reactivated. Memory response, or "Retest Reactivity", usually takes 2 to 3 days after coming in contact with the allergen, and can persist for 2 to 4 weeks.