When a pink, dome-shaped bump with a hard plug in the center suddenly appears on your mom’s forearm, it’s easy to panic—especially when it seems to grow noticeably within just a few weeks. 
One possibility doctors may consider is a keratoacanthoma, a skin growth that can develop surprisingly fast. But there’s an important reason not to ignore it: it can look very similar to squamous cell carcinoma, a type of skin cancer.
Keratoacanthomas often appear as firm, round, raised bumps on sun-exposed skin, including the forearms. The distinctive central plug is made of keratin and can give the lesion a rough, almost volcano-like appearance. 
While they’re more common in older adults and people with significant sun exposure, anyone who develops a rapidly changing skin lesion should have it professionally evaluated. Appearance alone cannot confirm what it is.
Until a doctor can examine it, the safest approach is surprisingly simple: leave it alone. Don’t squeeze, cut, pick, freeze, burn, or apply wart-removal acids to the bump. If clothing keeps rubbing against it, gently protect it with a clean, nonstick dressing. 
Taking one clear photo a day with a ruler nearby can also help document how quickly it changes. If it begins bleeding heavily, develops spreading redness, pus, severe pain, or fever, seek medical attention sooner.
The biggest message is this: don’t panic—but don’t ignore it either. 
A dermatologist may recommend a biopsy or removal because keratoacanthoma and squamous cell carcinoma can be difficult to distinguish without examining tissue. What looks like a frightening mystery at home can often be clarified with the right medical evaluation. Until then, protect the area, avoid experimenting with home treatments, and arrange an appointment as soon as reasonably possible. 
