Urticaria – also known as hives, weals, welts or nettle rash – is a raised, itchy rash that appears on the skin. It may appear on one part of the body or be spread across large areas.

The rash is usually very itchy and ranges in size from a few millimetres to the size of a hand.

Although the affected area may change in appearance within 24 hours, the rash usually settles within a few days.

Acute urticaria (also known as short-term urticaria) is a common condition, estimated to affect around one in five people at some point in their lives.

Urticaria occurs when a trigger causes high levels of histamine and other chemical messengers to be released in the skin.

These substances cause the blood vessels in the affected area of skin to open up (often resulting in redness or pinkness) and become leaky. This extra fluid in the tissues causes swelling and itchiness.