The reaction of the immune systems of the body to fight a chemical/s that are a threat to the health of the body. It exhibits as a reaction in the skin as a rash, swelling, itchiness, inflammation. An allergy, once developed, is for life.
Allergic contact dermatitis
![Allergic contact dermatitis](https://nailknowledge.org/wp-content/uploads/2021/01/Contact-allergy.jpg)