Watch: US Dermatologist Reveals One Nail Sign You Should Never Ignore

Nails can give important clues about your health and now a US-based dermatologist is "begging" her social media followers to check their nails for a vertical line, which could indicate a rare but serious type of skin cancer. In an Instagram video, Dr Lindsey Zubritsky asked her followers to check if they have a dark-pigmented vertical streak going down their nail. If yes, she urged users to get it checked immediately as it could indicate a subungual melanoma, which is a type of skin cancer. 

"It could potentially be a very serious form of skin cancer called a subungual melanoma," Dr Zubritsky said. "While it's not common, it can be easily missed if you don't know what you're looking for," she added. 

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A post shared by Lindsey Zubritsky, MD, FAAD (@dermguru)

Further, Dr Zubritsky said that not all dark streaks on nails are subungual melanomas or dangerous. A longitudinal melanonychia, for example, is a brown or black vertical nail streak that's typically benign, she explained. "It's more likely that you have the benign streak. It's a lighter streak. It's not changing. It's found on multiple nails," the dermatologist said. 

The doctor also drew the distinction between a subungual melanoma and a subungual hematoma, which is when blood pools under the nail after a trauma like getting a finger caught in a door or accidentally hitting it with a hammer. Hematomas typically grow out over time.

At the end of the video, Dr Zubritsky advised seeking medical help if you have the dark vertical line.  It could be evidence of a subungual melanoma, she said. 

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Notably, as per the New York Post, subungual melanomas account for only 0.7% to 3.5% of all malignant melanomas worldwide. A patient's chances depend on the stage of cancer at diagnosis and how far it is spread. 

The exact cause of subungual melanomas is not known, however, experts say that it doesn't seem to be linked to sun exposure. Having certain characteristics, including an age between 50 to 70, darker skin, and a family history of melanoma, put people at greater risk.

Subungual melanomas tend to affect the big toe and thumb the most, but they can also occur on any finger or toe.