Red patches on the skin: how to tell what they are

A red patch on the skin has a short list of causes, and two of them get made worse by the thing most people do first: apply a cream somebody recommended. Which cream, and which diagnosis, is the entire question.

What the patch is doing

• Ring-shaped with a raised, active border and clearer skin in the middle, slowly enlarging, itchy: ringworm. In India this is now the most common cause of a spreading red patch, and it is being seen far more often in adults than it used to be.
• Silvery scale on a well-defined red plaque over an elbow, a knee, the lower back or the scalp, with pitted nails: psoriasis.
• Ill-defined, dry, weeping or cracked, in the bend of an elbow or behind a knee, in someone with asthma or hay fever: eczema.
• Raised pink wheals that appear, itch furiously, move around and vanish within a day without leaving a mark: urticaria, hives.
• A single patch that is scaly, slightly brown and anaesthetic, with a thickened nerve nearby: that is leprosy, and it must be examined for, not assumed away.
• Red, hot, tender, spreading, with fever and swollen glands: cellulitis, a bacterial infection that needs antibiotics.
• A rash on the palms and soles, with painless mouth or genital ulcers and glands: secondary syphilis, and it is missed constantly because it does not itch.
• A large herald patch followed weeks later by many smaller oval patches in lines across the back: pityriasis rosea, which settles on its own.
• A photosensitive rash across the cheeks and the bridge of the nose, sparing the creases, with mouth ulcers and joint pain: lupus, and a rheumatologist.

The two that a steroid cream wrecks

• Ringworm treated with a combination steroid cream stops itching, looks paler, spreads wider, loses its ring shape, and comes back harder. That is tinea incognito, and it is the single commonest reason a treatable rash has been present for a year.
• Scabies treated with a steroid cream settles superficially while the mites continue, and the household gets it.
• Combination creams, the ones containing a steroid plus an antifungal plus an antibiotic, are the wrong tool for almost everything on this list. A plain antifungal in the right dose for the right length of time is what ringworm needs.
• Psoriasis, by contrast, is treated with topical steroids in the right strength for the right site, and stopping them suddenly can produce a severe rebound. Same symptom, opposite treatment, which is why the diagnosis comes first.

What we ask

• How long, how fast it has spread, and whether it started in one place or appeared everywhere.
• Itch, pain, burning, or nothing at all. Painless and uninflamed is a different list from furiously itchy.
• Anyone else at home with the same thing, and any pet with a patch of missing hair.
• The gym, the shared towel, the salon, the hostel, the long journey, and the new soap, dye, perfume or watch strap.
• What has already been applied, and whether a cream helped and then stopped helping.
• New medicines in the last month, including a painkiller, an antibiotic and a herbal packet, since a drug eruption can look like almost anything.
• Fever, joint pain, mouth or eye ulcers, weight loss, breathlessness, or a recent sore throat.
• Sun exposure, since several of these behave differently in daylight.

What we look at

• The shape, the border, whether it blanches under pressure, whether it is scaly, and whether the scale is silvery or fine.
• The distribution: symmetric points to an internal or allergic cause, one-sided and ring-shaped points to infection, sun-exposed areas point to photosensitivity.
• A scraping examined for fungus, which takes minutes and settles the biggest question on this page.
• The whole skin, not just the patch, including the scalp, nails, palms, soles and mouth.
• The glands, and a general examination, because a rash can be the visible part of a systemic illness.
• Bloods where the picture suggests them, and a biopsy for anything that has an unusual shape, is not responding, or has been present for months.

Red flags

• A red-purple rash that does not blanch under a glass, with fever, shivering and a person who is clearly unwell. That is septicaemia or meningococcal disease, and it is same-day emergency care.
• Blistering or peeling skin with fever, with mouth, eye or genital involvement, or after a new medicine. Stevens-Johnson syndrome and toxic epidermal necrolysis begin as a red patch and a sore mouth.
• Rapidly spreading redness with severe pain out of proportion to what is visible, with fever and a racing pulse. A deep infection, and it is an emergency.
• A widespread red, hot, shedding skin in a person who is shivering and unwell. Redness over most of the body is a medical admission.
• Crops of small pustules on red skin with fever, often after a steroid was stopped. Generalised pustular psoriasis.
• Any rash with breathlessness, facial or throat swelling, dizziness or a feeling of impending collapse. Anaphylaxis, immediately.
• A patch that is ulcerating, bleeding, hard, growing, or not healing in three weeks, which needs a biopsy rather than another cream.

What helps, once the cause is known

• Ringworm: a proper antifungal course for the full length, usually with a topical alongside, treating every lesion at once, and dealing with the source. Stopping when it looks clear is what produces the recurrence, and in extensive or resistant cases the dermatologist escalates.
• Eczema: emollients in quantity, on damp skin, every day, plus a topical steroid in the right strength for the site, used in a defined course rather than continuously, plus finding the trigger where there is one.
• Psoriasis: the right vehicle for the right site, keratolytics for thick plaques, phototherapy or systemic treatment for extensive disease, and the joint question asked at every visit.
• Urticaria: a non-drowsy antihistamine at the right dose, taken regularly through a bad period rather than only when the wheals appear, plus the trigger list, and emergency care for any throat or breathing involvement.
• Cellulitis: antibiotics, the limb elevated, and the portal of entry found, which is often a fungal infection between the toes or an unexamined wound.
• Itch in general: cool compresses, a fragrance-free wash, short lukewarm showers, cotton rather than synthetic against the skin, and nails kept short.

Where Ayurvedic care sits

• Khadira and manjistha as the classical skin pair, guduchi as the anti-inflammatory support, and panchatikta ghrita where the skin is dry, thick and scaly rather than weeping.
• Neem internally in a short defined course, and as a cooling application externally.
• Triphala gently through any long course, because the bowel is the first thing a long herbal prescription disturbs.
• As support alongside the treatment that suits the diagnosis, and reviewed at eight to twelve weeks like any other course.
• What it does not do is treat ringworm, cellulitis, a drug reaction, urticaria with angio-oedema, or an extensive psoriasis on its own, and a month spent trying is a month the rash has had to spread.

How we judge it

• Border and area, photographed in the same light, since a spreading patch is measurable and a subjective report is not.
• Itch at night, and how much sleep is being lost.
• Whether the scraping that was positive has become negative, which is the honest way to judge a fungal course.
• Whether anything that has not responded to a fair trial has been biopsied rather than given another cream, because persistence is a diagnosis, not a nuisance.