What to Know According to Dermatologists

At a recent skin cancer screening, my dermatologist asked me to show her any spots I was concerned about, which led me to a large “mole” on the back of my calf. I hadn’t had this one growing up and somehow it came out of nowhere, which I thought was concerning. “Oh that’s just a dermatofibroma,” she told me. “Sometimes you can get them from bug bites.” And down the rabbit hole I went. Turns out, I also have one on my shoulder blade where I was stung by a bee two years ago. But what is a dermatofibroma? And why do some people get them after insect bites? Let’s find out.

Featured Experts

• Sue Ellen Cox, MD, a board-certified dermatologist in Chapel Hill, NC
• Jessie Cheung, MD, a board-certified dermatologist in Chicago

What is a dermatofibroma?

“A dermatofibroma is a common, harmless growth made up of fibrous tissue in the skin,” says Chapel Hill, NC dermatologist Sue Ellen Cox, MD. “They often appear on the lower legs, but can show up on the arms, shoulders and other areas. Compared to a mole, which is usually smooth and evenly colored, a dermatofibroma tends to feel firm, may be dome-shaped, and can appear brown, reddish or slightly purple. A classic feature is that when you pinch the skin around it, the center dimples inward, which is something moles typically don’t do.” Chicago dermatologist Jessie Cheung, MD adds that these “harmless little bumps” may feel like a tiny marble under the skin and are basically a type of scar tissue.

What causes a dermatofibroma?

“Some people do seem more predisposed to getting them, especially women and those who get a lot of insect bites or have minor skin injuries such as from ingrown hairs from shaving,” says Dr. Cheung. “The exact ‘why’ isn’t fully understood, but the current thought is that dermatofibromas are a type of reactive process: the skin’s fibroblasts and immune system overreact to trauma, creating excess collagen and fibrous tissue.” They are also more common in adults than children.

Dr. Cox says that in some cases, a dermatofibroma forms as a reaction to minor trauma in the skin, such as a cut or insect bite. “The body essentially ‘overheals’ the injury by producing excess fibrous tissue. However, this doesn’t mean every insect bite will result in a dermatofibroma.”

Can they turn into skin cancer?

“No, dermatofibromas are benign and do not turn into skin cancer,” says Dr. Cox. “That said, sometimes other skin growths can look similar, so if one is changing rapidly in size or color, bleeding or causing pain, it’s worth a trip to the dermatologist it to be sure.” Dr. Cheung adds that dermatofibromas are usually stable over time, though their color can change.

Can you have a dermatofibroma removed? 

Dr. Cheung says this type of skin growth doesn’t need to be treated at all, but if it is itchy, sore or bothersome for cosmetic reasons, it can be removed. “Keep in mind though that the removal [usually through punch biopsy, the most common method] can leave a scar because the bump goes deep into the skin,” she advises. “Your dermatologist can also try shrinking your dermatofibroma with a steroid injection or by freezing it with liquid nitrogen.” Dr. Cox adds that in some cases, the resulting scar may be less cosmetically acceptable than the lesion itself, which is why some choose to leave these lesions untreated.”