There are a number of common issues that can lead to the formation of a yellow scab. One of the main culprits is impetigo, a bacterial infection that often affects children, which forms sores that usually then rupture and form a yellow crust on the skin. People who have seborrheic dermatitis, a condition that is normally confined to the scalp, may develop yellow scales and scabs at and above the hairline. The scabs that typically form at the site of a cold sore once it has blistered and then started to dry up can also be yellow.
Impetigo is a highly contagious condition, caused by Staphylococcus or Streptococcus bacteria, is particularly common in children, especially in settings where they are in close contact like school or day care. It typically starts as red sores or blisters around the mouth and nose. Once those sores rupture, they usually seep fluid, which then turns into a crusty yellowish scab. The condition can be allowed to clear on its own, which usually occurs within two or three weeks, or it may be treated with antibiotics if there is a concern it may lead to complications.
Another common cause for a yellow scab is a condition known as seborrheic dermatitis. This issue, which is sometimes mistaken for scalp psoriasis, can lead to the formation of yellow scales or crust that can attach to a person’s hair shafts, typically at or above the hairline. The lesions are normally fairly easy to remove but will recur without medical treatment. The skin of the scalp is also typically red, oily, and extremely itchy with this condition. It is generally necessary to use a special shampoo or other medication to treat seborrheic dermatitis.
People who get cold sores may also get yellow scabs on the face, often around the lips. Caused by the herpes simplex virus 1 (HSV-1), those who have been exposed typically have the virus lying dormant in their bodies throughout their lives. When the virus is triggered, it travels along the nerve endings to the person’s face where it causes tingling or pain before forming a red bump that subsequently blisters. As the blister or blisters begin to dry up, usually after several days, a scab or crust often forms in its place. This scab may last another couple of days before it then falls off on its own.