Black or very dark rash on the skin

Dark colour can come from post-inflammatory pigment, dried blood, a thick crust, bruising or reduced blood flow. Lighting and natural skin tone also affect how inflammation appears, so the texture and associated symptoms matter.

An itchy, dry rash that becomes darker after settling can occur with atopic or contact dermatitis. Psoriasis may form well-defined thickened plaques, while ringworm often develops an enlarging scaly edge. Moist skin folds can become inflamed through friction and trapped moisture.

Purple-black spots that do not lighten when pressed can represent bleeding beneath the skin. A hard black centre, loss of sensation, blisters, severe tenderness or surrounding swelling raises concern for deeper tissue damage rather than ordinary pigmentation.

Check whether the area lightens briefly under firm pressure, whether it is warm or painful, and whether new patches are appearing. Take photographs and note new medicines, illness, bites, injuries, heat exposure and products that touched the skin.

Keep the area clean, dry and protected from rubbing. Use an unperfumed moisturiser on intact dry skin, but do not scrub off crust, open blisters or apply bleaching agents. Avoid sharing towels if the rash has a scaly spreading border.

Seek emergency care for rapid blackening, severe or disproportionate pain, confusion, faintness, breathing difficulty, widespread blistering, or dark spots that do not fade under pressure alongside fever or feeling very unwell. Prompt care is needed for spreading warmth, pus, red streaking, loss of feeling or a rash near the eyes. Persistent unexplained patches also merit a clinical review.

Ask whether the colour represents pigment, blood, crust or reduced circulation; whether infection or a medicine reaction is possible; whether skin scraping, swabbing or blood tests would clarify the diagnosis; and which topical products are safe for the affected surface.