Many common skin rashes have similar characteristics, so it can be hard to tell them apart without a picture, but there are ways to narrow things down. The first thing you should consider is the location of the rash, since many tend to show up in specific areas. Other things you should consider are how the area feels — for instance, if it is itchy, scaly, or numb — and what the rash looks like. It's also important to note the color of the rash or the color of any discharge, since this can differ between rashes.
If possible, you should try to determine what caused the rash too. For instance, it might only happen after you eat certain foods or take certain medications, or it might happen after you go swimming. The more specific information you have about a rash, the easier it usually is to identify it. Though considering these characteristics can be helpful in identifying skin problems, you should consult with a doctor about any rash that comes on quickly, lasts for more than a few days, or is very itchy or painful.
Where the rash shows up on your body is often one of your best clues as to what it is. Many rashes usually only happen in specific parts of the body, like rosacea or athlete's foot. Others happen in specific patterns, like pityriasis rosea, which is sometimes called the "Christmas tree rash," since it tends to happen on people's backs in a Christmas tree shape. Sometimes the location can also give you a clue to what caused it. For instance, bacterial or fungal rashes tend to show up on places on the body that are wet and warm, like the groin or armpit.
Seeing that a rash has spread all over the body can be helpful too, since some are characterized by how fast they spread or the patterns in which they spread. For instance, eczema tends to happen on the insides of the elbows or the backs of the knees. You should also note what parts of your body aren't affected by the rash, since that could mean that something stopped it from spreading there. People often see this with contact dermatitis, that often only happens on exposed skin, or with swimmer's itch, which only happens on the parts of the skin that are directly in the water, not those that are covered by a swimsuit or bathing cap.
How the Rash Feels
Many common skin rashes are itchy, including ringworm, chicken pox, eczema, and impetigo. This can be because of an allergen, like the oil from a poison ivy plant, or because of a virus, as in the case of chicken pox. It's important not to scratch, since this can often spread the rash around the body or to other people. When trying to tell the difference between itchy rashes, you should consider the location as well as any other feelings that you get from the area, like a burning sensation or dry skin. Rashes like eczema and psoriasis tend to be itchy with dry skin, while hives or miliaria can be itchy and painful. A lack of feeling can also be an identifying sign — for instance, shingles is often burning or painful, but it can cause numbness, and a molluscum contagiosum rash is painless.
The texture of a rash can often be very helpful in identifying it. Skin rashes can be flat, rounded, have raised edges, have blisters or welts, or have thick, hard plaques. Flat skin rashes often come with some inflammation, but not blisters or welts; intertrigo is a good example of this. Many types have blisters, including dermatitis, shingles, eczema, and chicken pox. Sometimes a rash might have bumps instead of blisters, which are raised but not filled with fluid. If the rash is caused by a fungus and has a specific shape it often has raised edges, like ringworm.
The color of the area is important as well. Skin rashes are typically red, pink, or purple, but some also have white scales or plugs. If a rash mostly consists of redness and inflammation, it could be cellulitis, intertrigo, or athlete's foot, depending on the location. If it is only purple, it might be lichen planus. You should also note the color of any liquid or discharge; many have blisters filled with clear fluid, but impetigo blisters are filled with yellow fluid, molluscum contagiosum bumps can be filled with a white, cheesy substance, and rosacea can have pimples filled with pus.
Table of Common Skin Rashes
||The area touched by the allergen.
||Redness, swelling, blisters.
||Body, feet, groin, scalp.
||Raised red scaly rings.
||Blisters filled with clear fluid.
||Trunk or buttocks, but can be everywhere.
||Burning, tingly, painful, numb.
||Raised red dots and blisters.
||Raised red welts.
||Allergens, extreme temperatures, infection.
||Usually face, arms, legs.
||Blisters with yellow fluid.
||Skin exposed to water.
||Red bumps or blisters.
||Redness, inflammation, thick skin, pus-filled pimples.
||Knees, elbows, neck, etc.
||Oozing, bleeding blisters and thick patches.
||Allergens, climate, illness.
||Scalp, elbows, knees, lower back.
||Thick red plaques with white scales.
||Clear, fluid filled bumps.
||Red spots that spread.
||Warm, moist areas.
||Can be bacteria, fungus, or virus.
||Wrist or ankles, lower back, neck, legs.
||Purple or red bumps with flat tops.
||In children: face, trunk, armpits, extremities; in adults: groin.
||Flesh-colored bumps with a depression or white plug in the center.
||Chest, back, arms, legs.
||Pink scaly patches with raised borders.
||Redness, sometimes with blisters or sores.
Video 1 — Close ups of chickenpox on a child.
Video 2 — Information about how shingles develops.
Video 3 — Information about lichen planus.
Video 4 — Information about pityriasis rosea.
Video 5 — Information about psoriasis with pictures.
www.mayoclinic.com — A slideshow of common skin rashes with pictures and descriptions.
www.webmd.com — Another slideshow of common skin rashes and skin conditions.
www.chiff.com — Pictures of common skin rashes and information about treatment options.