It can be difficult to distinguish between different rashes, especially when the rash is transient.
Hives (urticaria) are characterized by an intensely itchy rash with red spots and flat swellings (wheals) on the skin. Sometimes the swelling may be pale with redness around it. The spots and wheals can be small or large and vary in size and shape. The wheals feel raised from the surrounding skin, but the surface itself feels smooth. The rash appears suddenly and often disappears just as quickly. The rash can occur anywhere on the body. Despite intense itching, there are no scratch marks on the skin. The skin does not peel, and after the rash has resolved, the skin appears normal. Another important characteristic is that each individual spot or wheal will disappear within 24 hours. However, new spots and wheals may come and go for several days (less commonly, over weeks).
There is a distinction between acute and chronic hives. Acute urticaria is characterized by spots or swellings (wheals) on the skin that appear quickly and usually disappear within 24 hours. They can continually appear in new locations over the following days and weeks. In a few cases, it can last for several years and cause significant distress. For most people, the symptoms will resolve after a few days or weeks. Chronic urticaria is characterized by repeated outbreaks over a long-term period, lasting more than six weeks.
Approximately 1 in 5 people will experience hives in their lifetime. The cause of the rash is the release of various chemical substances by immune cells in the dermis, with histamine being the most important. These substances bind to itch nerves in the skin and cause fluid leakage from blood vessels into the skin. The characteristic feature of urticaria is therefore itch and the development of flat, red swellings on the skin. It can be difficult to identify the exact triggering cause of acute urticaria. Often, no definite triggering cause is found. For the first episode, one can try to identify if anything different was used or done compared to usual. Sometimes, allergic reactions, infections, or medications can be the triggering cause. Other times, it can be heat, pressure on the skin, or substances applied to the skin.
The condition is rarely dangerous, and there are several effective treatments available. Antihistamines often have good effects and alleviate symptoms. These medications prevent immune cells from releasing histamine. It is common to take one or more tablets per day for an extended period. There are also other treatment options such as immunosuppressive treatment, injections, or medical light therapy (UV-B rays).
Eczema differs from hives in that eczema often has a rough and dry surface, which can flake, have small cracks (fissures), and ooze. Each patch lasts for several days to weeks/months if left untreated and does not resolve spontaneously within 24 hours.
Scabies can also cause intense itch but will not have wheals that come and go within 24 hours. With scabies, one often observes eczema-like rashes characterized by scratch marks. If examined closely, small millimeter-long lines (burrows) can sometimes be seen in the skin.
Rashes that occur with fever or respiratory infections usually do not cause intense itch and are not as transient as hives.
