Dermatologists constantly hammer home the message to check for new moles for any sign of skin cancer, but a new study suggests that the number of moles is not a good indicator of cancer’s aggressiveness. In fact, it might be the opposite.

According to research published Wednesday in the journal JAMA Dermatology, people with over 50 moles across their bodies have a dramatically reduced risk of developing more invasive melanoma. It’s people with just a handful of irregular moles who need to worry about deadly cancer the most.

Lead investigator Alan Geller, who studies risk factors for melanoma at the Harvard T.H. Chan School Of Public Health, emphasized “the importance of everybody having a baseline skin exam and paying particular attention to unusual moles on the skin.”

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“We are all at risk and we all need to be paying more vigilant attention to our skin,” he said.

Geller and his colleagues, with funding support from the drug giant Merck, surveyed 566 melanoma patients within three months of their diagnosis. To their surprise, they noted that most patients had few moles and no moles with unusual borders and color variations at the time the cancer was detected.

For patients under 60, they did find that people with six or more atypical moles at diagnosis tended to have thicker melanoma — a sign of deadliness, since the longer skin cancer goes unnoticed, the deeper it grows, and the worse the prognosis. In this younger age group, the presence of more than 50 total moles was associated with less thick melanoma.

There is no perfect explanation for these findings. According to Geller, melanoma may manifest with different levels of aggression in people with varying numbers of moles. People with a handful of atypical moles may also have a harder time monitoring their changes in size, shape, and color — especially since these moles can occur on your back or in places that are hard to see.

Pattern recognition could be key, Geller said: People with many regular-looking moles may be more likely spot an “ugly duckling” mole, because compared to the other moles, its appearance really stands out.  

Melanoma is the most lethal form of skin cancer, killing one American every 57 minutes. Given the fact that melanoma has a high cure rate, early detection is key.

Public health efforts are often focused on encouraging patients with multiple moles to seek out medical skin examinations, but experts worry that those practices may be discouraging people with fewer moles to request the same care.

“Patients often worry about having many moles, but this study shows that it’s not the total number of moles that is concerning, but the presence of atypical moles,” said Dr. Eleni Linos, a dermatologist at the University of California, San Francisco, who was not involved in the research.

“If you are concerned about an abnormal mole — one that is growing, changing, or bleeding — see a dermatologist to have it evaluated,“ she added.

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