Scabs are a defense against debris, infection, and blood loss. When you damage your skin and it bleeds, a blood clot forms. Eventually, the blood clot hardens into a crusty protective layer known as a scab. As the damaged tissue regenerates, it pushes out the scab, replacing it with new skin.
Typically, a scab is dark red or brown. As the scab ages, it becomes darker and may even turn black. A black scab typically does not mean anything more than the healing process is maturing.
A black scab does not signal infection. Signs of infection include:
- redness expanding around the wound
- swelling increasing around the wound
- pain or tenderness increasing around the wound
- pus draining from the wound
- red streaks spreading from the wound
- fever
Call your doctor if you observe any of these signs. Infections often require antibiotics.
It might take a few weeks, but minor wounds should heal on their own. The scab will eventually fall off. You might be able to speed the process by:
- Not picking the scab. Your scab will fall off naturally when it has completed its job of protecting the wound.
- Keeping the area clean. You can gently wash the area but do not touch the scab with unwashed hands.
- Moisturizing the area. Dry skin can slow the healing process.
- Using a warm compress. A warm compress can increase blood flow and help maintain moisture. It can also help relieve the itchiness that often comes with healing.
Under the right circumstances, any color scab can be a sign of skin cancer. This does not mean that every scab is a sign of skin cancer.
An open sore — perhaps with crusting or oozing areas — that heals and then comes back can be a sign of squamous cell or basal cell carcinoma.
Basal and squamous cells cancer tend to occur in areas on your skin that have been exposed to the sun. These areas commonly include the:
- backs of the hands
- face
- lips
- neck
If you have sores that won't heal or any new or changing skin growths, see your doctor right away.
Scabs are not particularly attractive, but they serve an important purpose. They defend wounds against debris and bacteria. If your scab is black, it's most likely a sign that it has been in place for enough time to dry out and lose its previous reddish brown hue.
If your wound doesn't completely heal, or heals and returns, call your doctor. Let them know if you're concerned about skin cancer.