Hives are welts; pink/swelling they can come up on any part of the skin. They itch and each individual hive lasts a few hours before fading away, leaving no trace. New hives appear as old ones fade. They can be any size from very small or join to cover broad areas of the body. The itch can be intense. In some people the hives burn or sting.
Angioedema is similar to hives, but the swelling occurs beneath the skin instead of on the surface. It generally lasts longer than hives, but the swelling usually goes away in less than 24 hours.
Acute: Hives lasting less than six weeks. The most common causes are certain foods, medicines, infections, insect bites and certain diseases.
Chronic: Hives lasting more than six weeks. The cause of this type of hives is usually more difficult to identify than those causing acute hives. For most people with chronic hives, the cause is unknown. Chronic hives can be controlled well in most people. Most cases of chronic hives resolve within five years.
Physical Hives: Hives caused by direct physical stimulation of the skin — for example, cold, heat, sun exposure, vibration, pressure, sweating, and exercise. The hives usually occur right where the skin was stimulated and rarely appear elsewhere.
Dermatographism: Hives that form after firmly stroking or scratching the skin. These hives can also occur along with other forms of hives.
Contact dermatitis is a form of skin inflammation that occurs when compounds touching your skin cause irritation or an allergic reaction. The red, itchy rash isn’t contagious or life-threatening, but it can be very uncomfortable.
Skin contact with soaps, cosmetics, fragrances, jewelry, or plants such as poison ivy or poison oak and some occupations involve exposure to substances that may cause contact dermatitis.
Diagnosis starts with a thorough medical history and exam. Patch testing will be recommended if contact dermatitis is suspected as the possible cause of the rash.
World Allergy Organization XXII World Allergy Congress: Abstract #3065. Presented December 6, 2011
Evaluation of patients using the Thin-Layer Rapid-Use Epicutaneous Test (TT, TRUE Test, Allerderm Laboratories) misses contact dermatitis responses in 12.5% of patients and only partially captures positive test results in 25.6%,"If you get a negative [TT] and you're still suspicious of contact dermatitis, you should refer your patient for further patch testing,”