Being aware of the first signs of skin conditions will help you know when it's time to visit a doctor. Here is a short refresher on five of the most important signs you might see. 1. Butterfly Rash This is a facial rash characterized by its shape: the middle part of the butterfly is on the bridge of the nose, with "wings" extending onto the cheeks. "It can signify a range of diseases, from milder conditions like rosacea, significant acne, eczema, and psoriasis, all the way to serious autoimmune connective tissue disorders such as lupus," says Joseph Jorizzo, MD, professor and founding chair of the dermatology department at the Wake Forest University School of Medicine in Salem, North Carolina. 2. Infections "Look for any sign of infection, such as a cold sore, which is characterized by a painful bump or blister on the face or nose," says Jill Weinstein, MD, clinical instructor of dermatology at Northwestern University in Chicago. "This may be caused by herpes simplex." Both viral and bacterial infections may appear as pustules, or tender lesions. They can sometimes look like acne, but may also be bigger or more isolated than a pimple, Weinstein says. 3. Patchy Hair Be alert for round, patchy areas of hair loss, which can be a sign of an autoimmune disease called alopecia areata, Jorizzo says. "Alopecia is associated with thyroid disease, but it can also be upsetting to the patient in and of itself," Jorizzo explains. "Prognosis is very good if there is just one little circle, but if they lose their eyebrows or eyelashes, or if it goes around the bottom of the scalp, the condition is likely to be more chronic." 4. Symptoms on the Nails Nails may also offer evidence of a medical condition. "Signs on the nails include a condition called clubbing, where there's body under the cuticle that changes the angle of the nail, so that it's like an upside down V," Jorizzo says. Clubbing is sometimes accompanied by edema, and the cuticle area may feel wet. It can be a symptom of several lung conditions, ranging from chronic bronchitis to lung cancer. Pits in the nails can be a sign of arthritis or psoriasis. Pits resemble a mere dent, perhaps 1 millimeter across. Jorizzo explains, "In psoriasis, the outer layers of skin turn over very quickly, and when they come from under the cuticle, little patches fall off, so you get a pit." Finally, a single dark black streak in the nail that comes up on to the cuticle can be a sign of melanoma. 5. Skin Cancer The most common source of skin cancer deaths is melanoma, which may be identified using the ABCDE criteria: Asymmetry. The mole is an unusual shape, not round. Border Irregularity. The edges of the mole may be jagged, scalloped, or wavy, or very sharp in one area. Color. The mole shows variation in color from one area to another. There may be multiple shades of tan, brown, black, white, blue, or red. Diameter. The mole is greater than 6 millimeters in diameter. Evolving. The mole is new, or an existing mole has changed in size, shape, or color. A more informal method of spotting a suspicious mole is called the Ugly Duckling Test: when a mole just seems to catch your attention for some reason. "The classic example is when someone has one thing on them that just doesn't look like any other spot on their body," explains Elizabeth Quigley, MD, a physician in the dermatology service at Memorial Sloan Kettering Cancer Center in New Jersey. "Let's say they have many black moles, but one brown mole. Or most of their moles are round and small, but they have one that is big and a different shape. That should be evaluated by a physician." The most common form of skin cancer is basal cell carcinoma. There are also some less common varieties that have different symptoms. "Basal cell carcinoma often presents in the form of shiny or pearly bumps, which patients think are pimples," says Quigley. If the lesion has been there for six months, and sometimes bleeds, that's a warning sign that it is not a pimple. Squamous cell carcinoma, responsible for about 20 percent of all skin cancer deaths, has symptoms that are quite different from those of melanoma. "Squamous cell carcinoma can present as firm bumps, scaly patches, or ulcers that don't get better. The skin is red and the scale is the kind that doesn't go away with moisturizer," Quigley says. "It's different from just dry skin, and the scale is usually thicker." She says squamous cells don't rub off like normal dry skin, and the scaly patch may bleed if it is removed by pulling or picking. Keep in mind that these are only guidelines, and you should have any concerns checked out by a qualified health-care professional. Knowing the warning signs can be valuable, but nothing replaces a doctor's expertise. John Otrompke is a health-care writer and consultant.