Mom has this fast-growing, dome-shaped pink bump with a hard plug in the center on her forearm. The clinic is closed for the weekend. What is this?

A fast-growing, dome-shaped pink bump with a hard plug in the center can be worrying, especially when it appears on a parent’s arm and the clinic is closed.

One possibility is a keratoacanthoma (KA), a rapidly growing, dome-shaped skin lesion that can develop a central plug of keratin—a hard, crusty material made by skin cells. However, squamous cell skin cancer can look very similar, and it is not possible to reliably distinguish the two from a description alone. Other skin conditions can also cause raised bumps or central plugs.

Because the bump is described as fast-growing, your mom should have it assessed promptly rather than waiting to see whether it disappears. I can explain what the possibilities are and what to do over the weekend, but a clinician would need to examine it—and may recommend a biopsy—to identify it accurately.

What might it be?

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The description is particularly consistent with a keratoacanthoma, a skin growth that often develops over a few weeks and can have a rounded, raised shape with a central hard keratin plug. It commonly appears on sun-exposed skin, including the arms and forearms.

Primary Care Dermatology Society

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The important concern is that keratoacanthoma can look very much like cutaneous squamous cell carcinoma (SCC), a type of skin cancer. Even a clinician may need a biopsy or removal and laboratory examination to tell them apart.

my.clevelandclinic.org

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Other possibilities include:

• An inflamed or ruptured cyst

• A wart-like skin growth

• A different type of skin tumor

The fast growth and central plug make it especially important not to assume it is a harmless cyst or wait for it to resolve on its own.

What should you do while the clinic is closed?

If your mom is otherwise feeling well and the bump is not bleeding heavily, severely painful, or showing signs of infection, this may not require an emergency department visit solely because the clinic is closed. However, arrange an in-person medical assessment as soon as the clinic opens, ideally with a dermatologist or a clinician experienced in evaluating skin lesions.

Until then: