An Allergic Reaction of the Skin.

Allergic contact dermatitis is an itchy skin condition caused by an reaction to agents that come in contact with the skin. This type of reaction occurs after the immune system processes the absorbed material and mounts an immune response against it. This reaction causes severe itching, swelling and redness in the affected area.  The first eruption may be delayed in its apprearance but future exposure to the agent responsible will cause reactions to appear within 24 hours.  Prescription medications are often necessary to control the process.  Poison ivy is a classic example of this condition.