You should see a dermatologist any time a skin, hair, or nail change persists for more than a few weeks, looks different from your other spots, or isn’t responding to over-the-counter treatments. Many people treat a dermatologist visit like a last resort, but earlier appointments almost always lead to simpler, less expensive treatment.
A Mole or Spot That Looks Different
Skin cancer is the single biggest reason not to delay a dermatology appointment. The standard screening tool is the ABCDE checklist from the National Cancer Institute: asymmetry (one half doesn’t match the other), irregular borders (ragged or blurred edges), uneven color (mixing shades of brown, black, tan, white, red, or blue), diameter larger than about 6 millimeters (roughly the size of a pencil eraser), and evolution (any visible change over weeks or months).
Beyond that checklist, pay attention to the “ugly duckling sign,” a mole that simply looks nothing like the others on your body. In a study published in JAMA Dermatology, nine dermatologists identified every melanoma in a group of 80 patients using this approach, and comparing a suspicious mole against a person’s other moles reduced unnecessary biopsies by nearly sevenfold compared to evaluating each spot in isolation. If one mole stands out as obviously different from the rest, that alone is worth a visit.
A Sore That Won’t Heal
Basal cell carcinoma, the most common form of skin cancer, often doesn’t look like a mole at all. It frequently appears as an open sore that bleeds, oozes, or crusts over. The sore may seem to heal for a while, then come right back. According to the Skin Cancer Foundation, any sore that persists for weeks or keeps recurring in the same spot is a warning sign. This is especially true on sun-exposed areas like the face, ears, neck, and hands. A quick biopsy in the office can rule it out or catch it early when treatment is simplest.
A Rash That Spreads or Comes With a Fever
Most rashes are mild and resolve on their own. The ones that need prompt attention share a few features: they spread rapidly, blister, or come with fever and general malaise. Drug reactions are a common culprit. While most medication-related rashes are harmless, rare severe forms can cause purple-colored spots on the chest and back, widespread blistering, or skin that peels in sheets. Fever alongside a new rash, especially if you recently started a medication, warrants same-day medical evaluation rather than a scheduled dermatology visit.
For rashes that aren’t urgent but won’t go away, a dermatologist can distinguish between conditions that look similar to an untrained eye but require very different treatments.
Persistent Patches of Itchy, Flaky, or Thickened Skin
Psoriasis and eczema are the two most common chronic skin conditions, and telling them apart matters because the treatments target different problems. Psoriasis produces thick, raised patches with silvery scales, usually on the scalp, elbows, knees, and lower back. The sensation is more burning or stinging than itching. Eczema tends to show up as red, rough, less clearly defined patches on the face, neck, hands, and skin folds, with intense itching that often worsens at night.
Psoriasis typically appears between ages 15 and 35 and is driven by an overactive immune system that accelerates skin cell growth. It can also lead to joint inflammation. Eczema often starts in childhood and is linked to a weakened skin barrier, frequently alongside asthma, hay fever, or food allergies. Over-the-counter moisturizers and hydrocortisone cream can manage mild flares of either condition, but if your symptoms keep returning, cover large areas of your body, or interfere with sleep, a dermatologist can offer targeted therapies that general practitioners typically don’t prescribe, including light therapy for psoriasis or immune-modulating treatments for severe eczema.
Sudden or Patchy Hair Loss
Losing 50 to 100 hairs a day is normal. What isn’t normal is finding clumps in the shower, noticing your part widening rapidly, or seeing smooth bald patches appear on your scalp. These patterns point to different conditions, and a dermatologist can often narrow down the cause with a physical exam and sometimes a small punch biopsy about 4 millimeters wide.
Some forms of hair loss are temporary, like the diffuse shedding that happens a few months after major stress, surgery, or childbirth. Others, like alopecia areata, produce coin-sized bald spots and need treatment to prevent progression. The most urgent category is scarring alopecia, where inflammation permanently destroys hair follicles. Conditions like lichen planopilaris and discoid lupus fall into this group. Biopsy is often crucial here because once the scarring is complete, the hair won’t grow back. Early treatment can preserve what’s left. If your hair loss is sudden, patchy, or accompanied by scalp redness, tenderness, or scaling, don’t wait.
Nail Changes You Can’t Explain
Nails offer a surprising window into your overall health. A dark streak running lengthwise through a nail can be a sign of melanoma under the nail bed, particularly if the streak is new, widening, or appears on only one nail. Pitting or crumbling of multiple nails sometimes signals psoriasis, even when no skin patches are visible yet. Nails that separate from the nail bed, develop horizontal ridges, or change color without an obvious injury are all worth having evaluated.
Skin Problems That Aren’t Responding to Treatment
If you’ve been treating acne, rosacea, or another skin condition with drugstore products for six to eight weeks without improvement, that’s a reasonable threshold to book an appointment. A dermatologist can prescribe stronger topical treatments, identify whether your self-diagnosis is actually correct, and check for underlying causes. Many people treat what they assume is acne for months only to learn it’s a fungal infection or rosacea, conditions that get worse with standard acne products.
The same logic applies to warts, recurring cysts, or fungal infections that keep coming back. Over-the-counter treatments work for mild cases, but persistent or painful growths may need in-office procedures. Cysts that are inflamed, infected, or located in areas that cause pain or restrict movement generally qualify as medically necessary removals rather than cosmetic procedures, which can affect whether your insurance covers the visit.
Annual Skin Checks
Even without a specific complaint, an annual full-body skin exam is worthwhile if you have risk factors for skin cancer: fair skin, a history of sunburns, a family history of melanoma, or a large number of moles (more than 50). During the exam, the dermatologist checks areas you can’t easily see yourself, including your scalp, back, and the soles of your feet. These visits take about 10 to 15 minutes and establish a baseline so that changes are easier to catch in future years.
If you have darker skin, skin cancer is less common but often diagnosed at a later stage because both patients and doctors may not be looking for it. Melanoma in people with darker skin tones disproportionately appears in less obvious locations like the palms, soles, and under the nails, making professional screening especially valuable.