Discoid (nummular) eczema

The name comes from the Latin nummus, a coin: the patches come out round or oval, with a sharply drawn edge, as though they had been traced round a rim. It is one of the forms of eczema, and it is exactly that shape which sets it apart from the others. It runs on for months, settles and comes back, often in the same place. Almost always it is taken for a fungal infection at first, treated with whatever comes to hand, and then it puzzles people by getting worse. Working out that this is what it actually is matters more than it seems: both the treatment and how long the whole thing lasts depend on it.

What shows up on the skin

It starts with a handful of small bumps and blisters on a limited area, most often on the shins, the forearms or the backs of the hands, less often on the trunk. Within a few days they run together into a solid plaque anywhere from the size of a coin to the size of a palm. The face and the scalp are usually left alone.

After that each patch follows the same course. First it weeps: clear fluid seeps out, the surface glistens and tiny blisters sit around the rim. A week or two later the weeping gives way to crusts, and the skin turns dry, thickened and cracked. Sometimes the middle clears while the edge stays raised, and that is the moment the plaque gets mistaken for ringworm.

The colour depends on the skin. On pale skin the patches are pink or red; on brown and black skin they come out purple, dark brown or, the other way round, paler than the surrounding skin, and redness there is genuinely hard to see. The itch is severe and always worse at night: plenty of people wake to find themselves scratching a leg in their sleep. There may be a single patch, though usually there are several, and the skin between them is dry, rough and tight.

What it gets confused with

Three mistakes are made here, and each one costs months.

• Ringworm. A fungal infection also draws rings. Telling them apart by eye can be impossible, and the price of getting it wrong is high: a steroid ointment takes the inflammation out of a fungal patch but also rubs out the features it is recognised by, so the patch spreads outwards and the picture becomes unreadable. If there is one plaque, growing at the edge and not responding at all to eczema treatment, the doctor has a simple way out: scrape off a few scales and look at them.
• Psoriasis. The plaques are thicker, the silvery scale comes away in sheets, the itch is milder, and the favoured sites are different: elbows, knees, lower back and scalp.
• A single stubborn plaque in an older person that has been there for months, itches little or not at all and responds to nothing. Behind that picture there may be Bowen's disease or a superficial form of skin cancer, and occasionally a cutaneous lymphoma that looks like ordinary eczema for years. What is needed there is not another cream but a dermatologist and a biopsy. It is uncommon, but it is precisely for that rarity that a patch behaving unlike the rest is worth showing to a doctor.

Why the skin behaves this way

Discoid eczema has no single cause. There is skin that has lost its defences, and there are the things that finish the job.

A healthy outer layer keeps water in and irritants out. When it dries out, the water escapes, gaps open between the cells, and substances the skin used to ignore start to provoke it: soap, bubble bath, washing powder, disinfectant solutions, wool, nickel. That is where the seasonal pattern comes from too, with flare-ups falling in the heating months, when the home is dry and it is cold outside. Warm, humid air, by contrast, usually settles things down.

It is often possible to identify the push that started it:

• a minor skin injury such as an insect bite, a scratch, a burn or a rub: the patch appears on that exact spot;
• constant contact with water and cleaning products, as in the hands of cooks, cleaners, health workers and hairdressers;
• poor blood flow in the leg veins, where eczema is common in any case;
• starting a new medicine; this has been described, but never stop something another doctor prescribed on your own initiative, take it up with them;
• a hot shower twice a day and regular alcohol, both of which dry the skin more than people expect.

Some of those affected have atopic eczema in their own past or in the family, but unlike that condition discoid eczema is not inherited and has no direct link with asthma or hay fever. It is never contagious in any circumstances: you cannot catch it in a swimming pool or off a towel.

When a patch becomes infected

Scratched skin is an open door. Bacterial infection announces itself by the patch suddenly behaving differently:

• it weeps heavily and the fluid turns cloudy or yellowish;
• a honey-coloured crust forms over it;
• the surrounding skin is hot, swollen and tender, and the redness pushes past the border of the plaque;
• fever, shivering, aching and a general feeling of illness set in.

That is a reason to be seen the same day. Hot redness spreading out around the patch together with a fever is already erysipelas or cellulitis, and those are treated with oral antibiotics, sometimes in hospital.

One picture is worth memorising separately, because it moves fast. If dozens of identical small blisters and dimpled sores erupt over the eczema within a day or two, the skin becomes sharply painful and a high fever develops, this may be eczema herpeticum: the cold sore virus spreading through damaged skin. Steroid ointments only make it worse here; antiviral treatment and a doctor are needed straight away, particularly if the face and eyelids are involved. It is rare, and it must not be missed.

The daily routine that carries half the result

In this condition emollients are not cosmetics but the mainstay of treatment. They rebuild the barrier without which any ointment works for nothing.

• Use the emollient constantly, including when the skin looks clear: gaps end in the patches coming back. Do not be sparing with it and do not rub it in, smooth it on in the direction the hair grows.
• The drier the skin, the greasier the product should be: an ointment holds moisture better than a lotion, though a cream sits more comfortably on inflamed, weeping areas. It is convenient to keep two: something light for the hands and something heavier for the body and for the night.
• Drop soap, shower gel, bubble bath and wet wipes altogether, even the ones that do not sting. Washing is done with a soap substitute emollient.
• A shower or bath every day, but warm rather than hot, and short. Afterwards pat the skin dry without rubbing and apply the product while the skin is still damp, before it starts to dry.
• Keep the nails short and, if the itch is fierce, wear cotton gloves in bed: people scratch themselves raw in their sleep and have no memory of it.
• Protect the skin from cuts and friction, because a fresh injury readily grows a fresh patch. Wear gloves for work with water, chemicals and soil.
• Greasy ointments soak into fabric and make it easily flammable: do not smoke or go near an open flame in impregnated clothing. Bath oils leave the tub slippery.

If a product that suited you for years suddenly starts to sting and irritate, there is no need to put up with it: find another formulation with a pharmacist or a doctor.

What the doctor prescribes

There is no remedy that cures discoid eczema outright, but bringing a flare under control and keeping the skin quiet for long stretches is entirely realistic.

• Topical corticosteroids. The backbone of flare treatment. This form of eczema usually needs a stronger preparation than the others, which is why the choice belongs to the doctor: a weak ointment on a thick plaque on the shin simply does nothing. It goes on the patch only, generally once a day, after the emollient and about half an hour behind it, and is kept up until the inflammation has gone. The side effects, meaning thinning of the skin, stretch marks, lasting colour change and increased hair growth, come with prolonged use of strong preparations over large areas; short prescribed courses do not usually produce them.
• Calcineurin inhibitors. Steroid-free ointments used where the skin is thin, or when steroids would otherwise be needed too often.
• Antihistamines. They do nothing for the skin itself and only partly touch the itch of eczema, but the older ones cause drowsiness and help people sleep through the night without scratching. For daytime use, the non-sedating ones are chosen if they are needed at all.
• Antibiotics. Only for proven infection: topical for one small patch, oral for widespread involvement. Smearing on antibiotic cream just in case achieves nothing and drives resistance.

When none of that holds the condition, a dermatologist may offer ultraviolet light treatment, medicated wet wraps or drugs that damp down the immune response, which call for monitoring and blood tests. If flares keep returning to the same spots or refuse to clear, patch testing is worth doing: sometimes an allergy to a specific substance sits behind the eczema, and finding it changes everything.

Be prepared to be patient: these patches respond more slowly than other kinds of eczema, and where they have healed, paler or darker marks stay for a long time and sometimes for good. That is not inflammation and not a reason to carry on with a steroid.

Online consultation

A remote appointment handles the central questions of this condition well: whether what is on the skin fits discoid eczema or whether it is fungal and needs looking at in person; whether the routine has been chosen sensibly; why a prescribed product has stopped working. The doctor goes through photographs of how the patches look and how they have changed, asks about work, washing habits and medicines, helps build a day-to-day plan and explains which changes mean an infection has joined in. The signs listed above as urgent are not assessed through a screen: those need someone to look at you in person the same day.

This material is for information only and does not replace medical advice.