What does the rash of acute urticaria look like?

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What does the rash of acute urticaria look like?

The rash usually appears suddenly and can affect any area of skin. Small raised areas called weals develop on the skin. The weals look like mild blisters and they are itchy. Each weal is white or red and is usually surrounded by a small red area of skin which is called a flare. The 'weal and flare' rash of urticaria looks similar to the rash caused by a nettle sting.

The weals are commonly 1-2 cm across but can vary in size. There may be just a few but sometimes many develop over various parts of the body. Sometimes weals that are next to each other join together to form larger ones. The weals can be any shape but are often circular.

As a weal fades, the surrounding flare remains for a while. This makes the affected area of skin look blotchy and red. The blotches then fade gradually and the skin returns to normal.

Each weal usually lasts less than 24 hours. However, as some fade away, others may appear. It can then seem as if the rash is moving around the body. The rash may appear quite dramatic if many areas of skin are suddenly affected.

Are there any other symptoms?

Most people with acute urticaria do not feel 'ill', but the appearance of the rash and the itch can be troublesome.
In some cases a condition called angio-oedema develops at the same time as urticaria. In this condition some fluid also leaks into deeper tissues under the skin which causes the tissues to swell.

- The swelling of angio-oedema can occur anywhere in the body but most commonly affects the eyelids, lips and genitals.
- Sometimes the tongue and throat are affected and become swollen. The swelling sometimes becomes bad enough to cause difficulty breathing.
- Symptoms of angio-oedema tend to last longer than urticarial weals. It may take up to three days for the swollen areas to subside and go.

A variation called 'vasculitic urticaria' occurs in a small number of cases. In this condition the weals last more than 24 hours, they are often painful, may become dark red, and may leave a red pigmented mark on the skin when the weal goes.