Insect sting allergy potentially something very serious and can lead to anaphylaxis, which is potentially life-threatening. The majority of individuals who receive a sting from an insect experience local reactions. It is estimated that 5-10% of individuals will experience a generalized systemic reaction that can involve symptoms ranging from hives to wheezing and even anaphylaxis. In the United States approximately 40 people die each year from anaphylaxis due to stinging insect allergy. Potentially life-threatening reactions occur in 3% of adults and 0.4–0.8% of children. A 2012 meta-analysis found that venom immunotherapy is an effective prophylactic treatment against insect bite and sting allergic reactions,
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.