What Causes Black Spots Under the Toenails?
May 12, 2022
Source: Cainiu Health
Dr. Liu Wan
Introduction
Minor blood vessels beneath the nail bed may rupture due to foot trauma or ill-fitting footwear, leading to localized bleeding that gradually darkens into black pinpoint spots or ecchymoses—appearing as black dots under the nail. These typically require no specific treatment and will be gradually absorbed and fade over time. Alternatively, accumulation of melanocytes at the nail matrix may result in excessive melanin production, potentially causing localized black spots. Melanocytic nevi (moles) on the nail may also slowly enlarge over time.
Black spots under the toenails may result from localized trauma causing subungual hematoma (blood accumulation beneath the nail). If the spot does not enlarge and gradually fades, there is generally no cause for concern. So, what causes black spots under the toenails?
What Causes Black Spots Under the Toenails?
Minor trauma to the foot—or ill-fitting footwear—can damage tiny blood vessels in the nail bed, leading to bleeding that subsequently darkens into black macules or patches visible beneath the nail. This condition typically requires no specific treatment; the discoloration will gradually resolve as the body reabsorbs the blood over time. Alternatively, melanocytes (pigment-producing cells) located at the nail matrix may accumulate and overproduce melanin, resulting in localized dark spots. A melanocytic nevus (mole) on the nail may slowly grow longitudinally over time, forming a dark streak along the nail plate—thus, close observation is advised.
Onychomycosis (fungal nail infection) may also induce melanin production, occasionally manifesting as small black spots on the toenail. Therefore, any black spot on the toenail warrants attention. However, if the spot results from traumatic subungual hemorrhage, it is usually benign and need not cause alarm; it will typically migrate outward gradually as the nail grows.
Nutritional deficiencies—including inadequate intake of vitamins or iron deficiency anemia—may also contribute to black spots under the toenails. Improving overall nutrition and supplementing with appropriate vitamins often helps resolve such changes. Importantly, black spots on the toenail must be evaluated carefully: whether due to melanoma or fungal infection, timely diagnosis and treatment are essential. Nail dystrophy associated with malnutrition, vitamin deficiency, or anemia can lead to subungual melanotic macules. As the toenail grows, such a spot may appear to elongate, producing a vertically oriented streak. We hope this information has been helpful!
