Figure 1. Allergic contact dermatitis to plaster.
Figure 2. Allergic reaction to flavine, spreading to other parts of the body.
The commonest manifestation is an itchy rash that develops over a few days, after skin contact with a substance. The affected area first becomes itchy, then red and swollen with vesicles (water bubbles).
Although usually confined to the area of contact, sometimes strikingly so (see Figure 1), the rash can spread to other parts of the body. (see Figure 2).
Occasionally the rash is more chronic, manifesting as an itchy patch that does not heal for weeks or even months. This usually occurs when there is frequent contact with the substance e.g. a watch strap . The rash resulting from contact allergy is called allergic contact dermatitis.