Spot Checker · Foot
Black spot on the Foot: Causes, Red Flags & When to Worry
Quick answer
A black spot on the foot is often a harmless blood blister caused by rubbing against tight shoes, or a simple darkened wart from walking barefoot in public places. However, it is important to check closely because a new, dark, or changing spot, especially on the sole or underneath a toenail, could be a red flag for a rare but serious skin cancer called melanoma. Always have a doctor examine any unusual dark mark on your foot to be safe.
Why a black spot on the foot is different
The feet are a frequently missed site for acral melanoma (especially on the sole and under the nail) as well as warts, fungal infections and pressure-related callus.
Skin issues on the feet behave differently due to unique anatomy and extreme daily friction. Because the soles rarely see daylight, typical sun-related moles are less likely. Instead, constant rubbing from walking in tight or sweaty shoes makes pooled blood beneath a nail or thick pressure calluses the most probable culprits. Communal showers also increase your risk for dark, pinpoint warts. While this hidden location avoids UV damage, it creates a false sense of security. The thick skin on the soles and the tight spaces under toenails are notorious, frequently missed hiding spots for acral melanoma, an aggressive skin cancer unrelated to sun exposure. Most new marks here are entirely harmless shoe-related injuries, but their secretive placement means you must routinely check your soles.
The most common day-to-day triggers in this area are tight or sweaty shoes, communal showers (warts, athlete's foot), repeated pressure points — each of which can produce or worsen a black spot here.
Most likely causes
Melanoma
Black, irregular spots — especially new or changing — must be checked promptly.
Seborrhoeic keratosis
Can appear very dark but has a waxy, stuck-on surface.
Blue naevus
Benign blue-black mole that has been stable for years.
Subungual haematoma
Blood under the nail from trauma — grows out with the nail.
Red flags — see a clinician
- •Any new black spot in an adult
- •Black streak under a fingernail or toenail (especially if it widens)
- •Changing colour, size, shape or texture
- •Bleeding, crusting or ulceration
Self-care while you decide
- ✓Get any new black spot assessed within 2–4 weeks
- ✓Do not attempt removal at home
- ✓Photograph and date any existing dark mole you want to monitor
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Check my black spot →Frequently Asked Questions
The most common causes are Melanoma, Seborrhoeic keratosis, Blue naevus, Subungual haematoma. Because the foot sees tight or sweaty shoes and communal showers (warts, athlete's foot), these triggers also raise the likelihood of a black spot appearing here.
Most black spots are harmless. However, you should seek a dermatology review if you notice: Any new black spot in an adult; Black streak under a fingernail or toenail (especially if it widens); Changing colour, size, shape or texture.
Use the ABCDE rule — Asymmetry, irregular Borders, multiple Colours, Diameter over 6 mm, and Evolution (any change). On the foot, also watch for sores that don't heal, pearly bumps with visible blood vessels, or any lesion that bleeds repeatedly. A free AI mole checker can help you track changes over time.
Try: Get any new black spot assessed within 2–4 weeks; Do not attempt removal at home; Photograph and date any existing dark mole you want to monitor. Avoid picking or squeezing, and photograph the area today so you can compare in 2–4 weeks.
Book a review if the spot is growing, changing colour, bleeding, painful, or persists more than 4–6 weeks. Same-day care is needed for spreading redness with fever, breathing trouble, or non-blanching purple spots.
Yes — our free AI mole and skin checker analyses a photo against thousands of dermatology images and flags ABCDE-style concerns within seconds. It is a screening aid, not a diagnosis, and we always recommend confirming any concerning result with a clinician.
Black spot elsewhere on the body
Medical disclaimer: This page is for general information and is not a substitute for professional medical advice, diagnosis or treatment. Always consult a qualified clinician about any concerning skin change. ScanSkinAI is a screening aid, not a diagnostic device.