If you have symptoms of anaphylaxis this is a medical emergency.Ĭall 999 immediately and ask for an ambulance if you or someone else is experiencing anaphylaxis. However, urticaria can occur in a severe allergic reaction called anaphylaxis. Urticaria on its own is not a serious condition. In these cases, the raised areas or weals last longer than 24 hours, are more painful, and can leave a bruise. chronic urticaria – in rarer cases, where the rash persists or comes and goes for more than six weeks, often over many yearsĪ much rarer type of urticaria, known as urticarial vasculitis, can cause blood vessels inside the skin to become inflamed.acute urticaria – if the rash clears completely within six weeks (most cases last 24 to 48 hours).The raised areas can range from a few millimetres to the size of a hand. Urticaria rash can be in one place or spread through the body
