Dark, black or blue toes: what the color can mean

Reading the color: a quick guide

Where the color sits, how fast it came and how the rest of the foot feels help sort out the cause. Use this table as a starting point, not a diagnosis.

Blood under the toenail

Bleeding under the nail, called a subungual hematoma, is the most common cause of a dark nail, and many people don’t recall an injury.⁠^[1] A blow or crush bleeds into the nail bed, and the trapped blood presses on it, which can be very painful. A tiny hole in the nail (trephination) relieves most; a large one, or a cut in the nail bed, may need the nail removed and the bed repaired.⁠^[2] An X-ray checks for a break in the tip of the toe bone, which often goes with it;⁠^[2] we take X-rays on site.

If the dark patch doesn’t move out with the nail, it needs a closer look, because a melanoma can bleed too.⁠^[1]

A dark stripe or changing spot: checking for melanoma

A brown or black band along a nail has many causes, including old blood, fungus, some medicines and harmless clusters of pigment cells. Most are benign, but each deserves a check.⁠^[1] The one not to miss is nail melanoma: it is often misdiagnosed for years, and that delay is linked to a poorer outlook.⁠^[1] Warning features include:

• a black band, or several shades in one band
• irregular borders, or a width of 3 mm or more
• a band that is changing
• pigment spreading onto the skin around the nail (Hutchinson’s sign)
• bleeding or a sore at the nail⁠^[1]

These call for prompt referral to a dermatologist for a biopsy of the nail matrix, where the nail grows from.⁠^[1]

Melanoma can also start in the skin. Its least common type usually appears on the palms, the soles or under the nails, so have a dark spot on a toe or sole checked if it is new, uneven in shape or color, or changing.⁠^[8]

With diabetes: a dark spot in a callus

On a numb foot, a bent toe or a bony spot takes extra pressure and the skin thickens into callus. The callus raises the pressure further, often with bleeding beneath it, until an ulcer forms.⁠^[9] The prevention guideline counts bleeding, blisters and cracks as pre-ulcer signs that appear to strongly predict an ulcer and need treatment right away.⁠^[10]

We trim the callus, look underneath and take pressure off the spot. For a flexible hammertoe with a pre-ulcer sign at its tip, the guideline suggests considering a small release of the tendon that curls the toe (flexor tenotomy), or a toe orthotic;⁠^[10] Dr. Ozturk performs these releases and other toe-straightening surgery. See ulcers from bent toes and bony prominences and surgery that takes pressure off ulcers.

Pale, dusky or blue toes: a circulation warning

In peripheral artery disease (PAD), plaque narrows the leg arteries. A foot short of blood may feel colder than the other, look pale, discolored or blue, and stop growing toenails and leg hair.⁠^[3]

PAD together with pain at rest, gangrene, or a leg or foot sore present for more than 2 weeks is called chronic limb-threatening ischemia (CLTI). Anyone suspected of having it should be referred urgently to a vascular specialist.⁠^[11] In CLTI the color usually shifts with position: the foot turns pale when raised and red when it hangs down.⁠^[11] With diabetes, nerve damage can mask the pain and even leave the foot feeling warm.⁠^[4]

A sudden change is different. Acute limb ischemia is a drop in blood flow that has come on within the past 2 weeks; the foot can turn cold, pale, painful or numb, and it is a vascular emergency.⁠^[7] Call 911 or go to the emergency department.

Vascular specialists restore blood flow; we refer you, coordinate the timing, and carry on with wound care and any foot surgery. See peripheral artery disease and foot pain at night, or our sister practice’s guide to cold feet or numb feet (external site).

Blue toe syndrome: plaque debris in the toe arteries

In blue toe syndrome, one or more toes turn blue or purple, often while the foot pulses can still be felt. Cholesterol crystals and other plaque debris break off in a large artery such as the aorta and lodge in the small toe arteries, usually more gradually than a blood clot does. It often follows a procedure done inside an artery but can happen on its own, and the same debris can reach the kidneys, gut, eyes and brain.⁠^[5]

These toes need same-day medical care, not only foot care, and emergency care if the color changed suddenly or the foot is cold or pale. If a sore opens, we treat it with regular wound care visits.

Black skin: when tissue has died

Gangrene is the death of tissue, and when it involves the skin, the skin turns blue or black. Diabetes and blood vessel disease raise the risk.⁠^[6] Dry gangrene follows slowly failing circulation and shows mostly in the toes. Wet gangrene is infected dead tissue, often swollen and red, with pus.⁠^[12] If the whole foot is red, hot and swollen, see a red, hot, swollen foot.

Gangrene needs urgent evaluation, and dead tissue generally has to be removed so the healthy tissue around it can heal.⁠^[6] This is where surgery saves the foot. For wet gangrene in a foot with poor circulation, the global vascular guideline calls for urgent surgery to drain infection and remove dead tissue, plus antibiotics.⁠^[11] When gangrene comes from failing circulation, most people are assessed for a minor amputation, such as of a toe, once blood flow has been restored.⁠^[7]

Dr. Efe Ozturk, a Foot and Ankle Surgeon, is board certified in wound care (FAPWH). For the feet that need it, he removes dead tissue and performs toe, ray, transmetatarsal and midfoot amputations at a level that can heal, keeping as much of the foot as possible. See gangrene and toe and partial foot amputation. If you have been told you need an amputation, read what a limb salvage second opinion involves.

Frostbite

Frostbite freezes skin and the tissue beneath it, most often in the toes, fingers and ears, and badly injured tissue can turn black.⁠^[13] Don’t rub frozen toes or warm them by a fire or heater, and don’t thaw them if they could freeze again.⁠^[13] Unless there is infection or severe damage, surgery is often delayed until the line between living and dead tissue is clear, sometimes weeks to months, to keep as much of the foot as possible.⁠^[13]

How we find the cause

We start with the story: when the color changed, any injury, cold exposure or recent procedure, and your health history. Then we examine both feet and the pulses. With diabetes and a foot sore or gangrene, the international guideline on artery disease adds Doppler waveforms and the ankle-brachial and toe-brachial indexes, because no single test or reading can rule artery disease out.⁠^[4] We do noninvasive circulation testing at our practice and take X-rays on site; arterial duplex ultrasound or angiography is arranged with vascular specialists. See circulation tests for foot wounds.

If diabetes has put your feet at risk, check them daily and contact a trained professional quickly about any sore or sign of one forming.⁠^[10] Our parent practice’s daily foot check guide (external site) shows how.

When to seek care

See us within a day or two for any foot wound that isn’t healing, especially if you have diabetes.