It should be understood that hives caused by anything can show up on any part of the body at any time, so having hives on knees and elbows is not necessarily any more or less common than having them appear somewhere else. But there is anecdotal evidence that points strongly to hives on knees and elbows being caused by an allergic reaction. Allergic reactions, contrary to popular belief, are not the most common cause of hives. Of those cases that are diagnosed, most of them are found to be caused by a virus or some other infection.
But for some reason hives behind knees, or hives on knees and elbows are most commonly the result of an allergic reaction. So if this applies to you, the obvious job for you is to see if something you ate or something you have come in contact with is causing these hives. Some people find that keeping a journal or diary of your food intake and activities will help you narrow it down if the allergen is not readily apparent. But there are some other conditions that either mimic hives, or resemble hives and cause hives on knees and elbows. Some of these are explored below.
Angioedema Most Closely Resembles Hives
Angioedema is swelling that that affects the deeper layers of the skin but closely resembles hives. And in the most common of the acute cases triggered by allergens, angioedema starts in many times with hives on knees and elbows. The hives of angioedema is usually not as itchy as common hives, but the swelling and pain can be worse with these hives. Knees and other joints can become more painful. Food and drugs are common triggers.
Contact Dermatitis Can Mimic Hives As Well
Contact dermatitis happens when certain substances come into contact with the skin and cause a rash. This rash can look very similar to hives. And the reaction can look like hives on knees and elbows in particular. Because the contact causes the rash, it occurs often on the knees and elbows because we naturally kneel or lean and rest with our elbows, which become the first area of contact. Poison ivy is an example of this type reaction. The best treatment is to wash the area thoroughly as soon as possible to avoid spreading further.
A cold soak or cold compress will relieve the itching, as will some lotions and ointments.
Similar to contact dermatitis is eczema, which is also triggered by allergens. The rash is a little more scaly and red but can look similar to hives on knees and elbows. Do not scratch eczema and treat it the same way as contact dermatitis.