Hives are the welts, or wheals, that people get when they have urticaria. Urticaria is a common condition that occurs in up to 20 percent of the population at one time or another. It can affect any person of any race at any age on any part of the body in any season of the year, but it often shows up in the evening or in the morning (just after waking). Itching can occur and is typically worse at night, which can interfere with sleeping. Sometimes hives may also sting or hurt. Hives can be very small (such as the size of the tip of a pen) to very large (such as the size of a dinner plate).

In this gallery of hives pictures, you will find various photos of different types of hives and the important characteristics of each. This first picture shows what a typical case of hives looks like.

Hives Caused by Infection

Hives are considered to be idiopathic, meaning that an outbreak can happen spontaneously and the cause isn't always known. If a cause can be found, the most common cause is an infection. Other possible causes include an allergic reaction, stress, exercise, sun exposure, pressure on the skin, scratching, and chemical exposure. This photo is an example of hives caused by a viral infection.

Chronic Hives

Hives on Abdomen — Heather L. Brannon, MD

Hives are usually diagnosed based on their appearance, so a lot of expensive blood or skin tests are typically not required. However, if you have repeated cases of acute hives or a chronic case of hives and the cause isn't obvious, more testing may be needed to figure out what may be triggering the condition. A doctor may recommend taking an antihistamine to relieve the itching, or he or she may advise taking a different medication to treat the hives. Fortunately, most cases of hives resolve on their own.

Acute Hives

Urticaria rash (hives) on legs due to exam stress — DR P. MARAZZI/SCIENCE PHOTO LIBRARY / Getty Images

Hives are classified as either acute or chronic, depending on whether they've been present for fewer than or more than six weeks. This is a picture of a case of acute hives. Chronic hives often don't look like hives—they tend to look more like red places that someone has scratched.

Spongy Hives

When something causes skin cells to release histamine, capillaries (thin blood vessels) leak fluid into the top layer of the skin, the epidermis. This causes parts of the skin to swell and turn into what are called hives. Depending on the amount of fluid that gets released, hives can look very "spongy" like this. Compare this picture to the next photo of hives.

Flat Hives

Hives - Urticaria, Skin Disease — anand purohit / Getty Images

Hives develop due to a complicated chain of events that results in the release of histamine into the surrounding tissue. Histamine causes the blood vessels to leak, so fluid accumulates in the skin. Depending on the amount of fluid that leaks and the part of the skin it leaks into, hives can be thick and "spongy" like the previous picture. Or they can be relatively flat like these hives.

Overlapping Polycircular Hives

Overlapping Hives — Heather L. Brannon, MD

The shape of hives is described as polycircular. This means that they are made up of many circles. Can you pick out the overlapping circles in this picture of hives? See the next picture for the results.

Polycircular Hives Identified

Here, with this drawing on top of the photo, you can see the multiple circles that make up a typical case of hives. Now that you've looked at all of these different hives pictures, are you itchy yet?