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Black Toenail: 5 Possible Causes and Preventive Measures

Medically reviewed by Jezreel Esguerra, MD · General Practitioner

Written by Lorraine Bunag, R.N. · Updated Feb 16, 2023

    Black Toenail: 5 Possible Causes and Preventive Measures

    A black toenail is common after an injury to the toe as blood pools under the nail. The good news is, the discoloration will most likely disappear as the injury heals. But, what if you develop a black toenail without experiencing some kind of injury? Should you be worried? In this article, we will talk about the possible causes of black toenail and ways to prevent it. 

    Possible Causes of Black Toenail

    If you have a black toenail, consider the following possible causes:

    1. Poorly-Fitting Shoes

    We mostly associate nail injury with blunt force trauma, which typically happens when we drop something heavy and hard on the toe or we bump our toe hard somewhere. 

    But blunt force trauma isn’t the only injury that can befall our toes. 

    Do you have a black toenail but do not remember injuring your foot? Then, think about poorly-fitting shoes. Wearing shoes one size smaller can lead to a black toenail. 

    2. Repetitive Trauma

    If it’s not blunt force trauma or poorly-fitting shoes, consider repetitive trauma from hiking or running. 

    Experts say your toes receive “quite a beating” as your feet pound the pavement when you run. Running also causes your toes to bump at the front or side of the shoes. 

    The descent during a hike is also traumatic for the toes since they forcefully bump on the shoes. 

    Hence, if you recently ran or hiked, or are a runner or hiker, to begin with, having a black toenail is expected. 

    3. Fungal Infections

    Fungal infections often lead to white or yellow nails. However, black toenails can also occur due to debris buildup. 

    Other symptoms that might clue you in a fungal infection are: 

    • Thickened nails
    • Nails that are brittle or “crumbly”
    • Distorted nail shape
    • Toes smelling slightly foul

    Learn more about nail fungus infection here:

    4. Melanoma

    In some cases, a black toenail points to melanoma, the most serious type of skin cancer. 

    Melanoma might cause an irregular patch of darkened skin, which can occur under the nail. Note that if it’s melanoma, it’s unlikely that the whole nail is darkened. You might see a streak of black on the nail, commonly on the big toe. 

    Other signs of melanoma include a dark patch of skin on the side of the nail, nail splitting, bump under the nail, and nail lifting

    If you see these signs, consult your doctor as soon as possible. 

    5. Underlying Health Condition

    Finally, a black toenail can also occur if you have an underlying health condition, such as diabetes, heart disease, kidney disease, and anemia. 

    If this is the case, then treating your condition should take priority. 

    How To Prevent Having Black Toenails

    The best way to prevent having a black toenail is to eliminate the cause. 

    Take steps to prevent nail fungus by:

    • Keeping your feet and toes clean and dry
    • Changing socks throughout the day if you’re prone to sweating. Alternatively, you can also purchase sweat-absorbing socks. 
    • Wearing shoes made of breathable material

    If you run or hike, consider the following preventive measures:

    • Trim your toenails regularly. The shorter your toenails are, the less likely they will bump on the side and front of the shoes. 
    • Consider silicone pads for shoes. They might help absorb pressure when running. 
    • Choose appropriate and well-fitting shoes. Visit a store that specializes in running and hiking shoes, so the attendants can give you professional advice. Often, the goal is to choose shoes that give enough room for the toes, but not too much that your foot slides. You also need to consider how they fit with the socks on. 

    If your black toenail doesn’t get better or when you have other concerns, don’t hesitate to consult a dermatologist. 

    Learn more about Nail Care here


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    Jezreel Esguerra, MD

    General Practitioner

    Written by Lorraine Bunag, R.N. · Updated Feb 16, 2023

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