Rash

Skin is the one area where remote assessment is often better than an in-person appointment. A clear photograph taken in daylight can be looked at twice, compared over time, and shown to a colleague — none of which is true of a rash glimpsed across a desk in a ten-minute appointment.

What matters diagnostically is less the redness than the distribution, the shape of individual lesions, whether it itches, and what happened just before it appeared.

Itchy and long-standing — eczema in the elbow and knee creases; psoriasis as raised plaques with silvery scale on elbows, knees and scalp; contact dermatitis, which follows the shape of whatever touched it.

Itchy and recent — hives, as weals that move around and fade within a day; scabies, intensely itchy and much worse at night, with others in the house itching too.

Shaped or patterned — ringworm, a ring with a raised scaly edge; shingles, a painful band on one side that does not cross the midline; impetigo, with golden crusts.

After something — viral rashes, common and self-limiting, particularly in children; drug reactions, typically 1 to 2 weeks after starting something new.

The one to know — a non-blanching rash, which does not fade under pressure. That is a bleeding-into-the-skin pattern and always needs urgent assessment.

Send photographs before your appointment. Natural daylight, no flash, one wide shot showing the distribution and one close-up. Include something for scale if the size matters. That combination gives more information than most in-person descriptions.

The consultation covers what appeared first and where, whether it itches, what you have started taking or using, and whether anyone else is affected — the last question settles scabies and infectious rashes quickly.

Most rashes need treatment rather than testing. Where testing helps we arrange allergy testing, inflammatory markers, or skin swabs, and prescriptions go to your pharmacy the same day.

What we cannot do is feel the texture of a lesion or examine a mole with a dermatoscope. Any changing mole needs in-person dermatology assessment, and we will arrange it.

How do I take a photograph that is actually useful?

Three things, and they make more difference than any camera:

• Daylight, no flash. Stand near a window. Flash flattens colour and hides texture
• Three distances — a wide shot showing the body part, a mid shot showing the pattern, and a close-up from around 20cm
• A coin in frame for scale, and a repeat photograph a couple of days later so we can see how it is changing

Skin is the specialty best suited to remote assessment — provided the images are good, a video consultation is close to as informative as being in the room.

Is it an allergy?

Less often than people assume. True allergic rashes come on quickly, usually itch intensely, and often take the form of raised weals that move around the body and individually last less than a day. A rash that has crept on over weeks, sits in the same place, and is scaly rather than raised is very unlikely to be an allergy — eczema, psoriasis and fungal infection are far commoner.

Should I take an antihistamine?

Worth trying, but know what it does. Antihistamines work well for hives and allergic itch, and poorly for eczema, psoriasis and fungal rashes, where histamine is not driving the itch. A non-drowsy one such as cetirizine or loratadine is a reasonable first step; sedating ones taken at night can help sleep when scratching is the problem.

Should I just use a steroid cream?

Sometimes exactly right, sometimes the worst thing you could do. Steroid cream on a fungal infection suppresses the redness while letting the fungus spread, producing an altered, ring-like rash that is then hard to identify. If a rash is not clearly eczema, get it identified before reaching for hydrocortisone — and if a rash improves on steroid then flares worse each time you stop, suspect fungus.

My rash doesn't look red. Does that rule things out?

No — and this is important on brown and black skin. Inflammation that appears red or pink on white skin frequently appears violet, grey, dark brown or simply darker than the surrounding skin on deeper skin tones, and much medical teaching material does not show this. Cellulitis, eczema and drug rashes are all routinely missed for this reason. Judge by warmth, swelling, texture and change — not by whether something looks red.

What does a drug rash look like?

Typically widespread small red or dark spots merging into patches, starting on the trunk and spreading outwards, appearing 5 to 14 days after starting a new medicine — often after a course has already finished, which is why the link is missed. It usually itches and settles within a week or two of stopping the drug.

The warning signs that make it an emergency: blistering or skin peeling away, sores in the mouth, eyes or genitals, facial swelling, fever, or feeling systemically unwell. Those need A&E the same day.

Is it contagious?

Depends entirely what it is. Contagious: impetigo, scabies, chickenpox, fungal infections such as ringworm and athlete's foot, and viral warts. Not contagious: eczema, psoriasis, hives, and drug reactions — despite the assumptions people make about them.

When does a rash count as an emergency?

Five situations, all of which mean 999 or A&E rather than an appointment: a rash that does not fade under a glass; swelling of the face, lips or tongue with breathing difficulty; blistering or peeling skin with mouth, eye or genital sores; a rapidly spreading rash with fever and confusion; or an area of skin that is intensely painful out of all proportion to how it looks.

Everything else — which is the vast majority of rashes — can be assessed calmly, and often very well, with good photographs and a dermatology consultation.