More than 11 moles on an arm may be ‘sign of skin cancer risk’

“More than 11 moles on right arm ‘could indicate greater skin cancer risk’,” The Guardian reports. 

You should check your skin every few months for any new moles or changes to existing moles

A new study found that people with 11 or more moles on their arm were likely to have over 100 moles on their body – a known risk factor for the melanoma type of skin cancer.

Counting the entire number of moles can be time-consuming for clinicians and difficult for an individual to do by themselves. Researchers wanted to see if there was a handy proxy that would predict with a reasonable degree of accuracy a person’s total mole count.

Using data mainly from twin studies, their key finding was that women with more than 11 moles on their right arm had approximately nine times the risk of having more than 100 moles on their body, compared to women with less than 11.

Most of the data was taken from studies of white women, so the findings may be less applicable to men, and can’t be generalised to other ethnicities.

There is little you can do about the number of moles you have, but you can reduce your risk of skin cancer. The best way to prevent all types of skin cancer is to avoid overexposure to the sun, as well as UV tanning lamps and beds.

The ABCDE of melanomas

A helpful way to tell the difference between a normal mole and a melanoma is the ABCDE checklist:

  • Asymmetrical – melanomas have two very different halves and are an irregular shape.
  • Border – melanomas have a notched or ragged border.
  • Colours – melanomas will be a mix of two or more colours.
  • Diameter – melanomas are larger than 6mm (1/4 inch) in diameter.
  • Enlargement or elevation – a mole that changes size over time is more likely to be a melanoma.

If you are concerned about the appearance of a new, suspicious-looking mole, or a change in appearance to an existing mole, then see your GP.

Where did the story come from?

The study was carried out by researchers from King’s College London, University of Turin (Italy), Imperial College London, London North West Healthcare NHS Trust and West Herts NHS Trust. It was funded by the Wellcome Trust.

The study was published in the peer-reviewed British Journal of Dermatology on an open-access basis, so it is free to read online or download as a PDF.

Most of the UK media’s reporting of this study was accurate.

Many reports added balance with a quote from Dr Claire Knight, of Cancer Research UK, who said: “This study suggests that the number of moles on our arms gives a good indication of how many moles we have on our bodies. This could be helpful, because we know that people with lots of moles have a higher risk of melanoma.”

She adds: “Other risk factors for melanoma include having red or fair hair, fair skin, light-coloured eyes or having been sunburnt in the past.”

She cautioned about focusing too much on the arm and neglecting the rest of the body, saying: “less than half of melanomas develop from existing moles. So it’s important to know what’s normal for your skin and to tell your doctor about any change in the size, shape, colour or feel of a mole or a normal patch of skin. And don’t just look at your arms – melanoma can develop anywhere on the body, and is most common on the trunk in men and the legs in women.”

The Daily Telegraph reported a quote from one of the lead authors, Simone Ribero, who said, “The findings could have a significant impact for primary care, allowing GPs to more accurately estimate the total number of moles in a patient extremely quickly via an easily accessible body part. This would mean that more patients at risk of melanoma can be identified and monitored.”

What kind of research was this?

This was a large cross-sectional study of healthy UK Caucasian female twins. The study aimed to estimate a predictive value for moles on 17 different body sites to estimate total body mole count. This information was used to estimate a cut-off value of mole count on a particular body part (like an arm, a leg, or the back) that best predicted the presence of more than 50 or more than 100 moles.

The researchers said that total body mole count is one of the important risk factors for developing melanoma.

Melanoma is a type of skin cancer that can spread to other organs in the body. The most common sign of it is the appearance of a new mole or physical changes in an existing mole. This can happen anywhere on the body, but the back, legs, arms and face are most commonly affected.

Cross-sectional studies which include a large population with a long follow-up period can tell us if there is any association between an exposure and an outcome, but this alone cannot show if there is a direct causality.

What did the research involve?

This research included 3,694 Caucasian female twins from the ongoing TwinsUK study. A skin examination by a trained nurse provided data on their skin type, hair and eye colour, and freckles, as well as mole count on 17 body sites.

To demonstrate that the findings from the TwinsUK study can be applied to other healthy Caucasian populations in the UK, researchers replicated the study in 415 healthy adults (161 males and 254 females).

The researchers calculated how well mole counts on each body site correlated with total body mole count, and at different thresholds (more than 50 and more than 100 total mole count), and whether this was linked to a higher risk of cancer. Results were adjusted for common confounders such as age, height and skin type.

Out of the 3,694 twin females, only 2,854 were included in the analysis due to missing data on 840 women. The average age was 47 and the average body mole count was 32. The average age in the replication group was 45, while the average body mole count was 33 in men and 35 in women.

What were the basic results?

Out of 2,854 twins, 582 (20.4%) had a total body mole count of more than 50, and 187 (6.5%) had a total body mole count of more than 100.

The most accurate threshold for predicting more than 50 and more than 100 moles was having more than seven, or more than 11, moles on the right arm respectively for both men and women. Interestingly, there was no difference in the predictive ability of using the whole right arm, or just the section above the elbow.

Women with more than seven moles on their right arm had approximately nine times the risk of having more than 50 moles altogether, compared to women with less (odds ratio [OR] 8.81, confidence interval [CL] 7.03 to 11.04).

Women with more than 11 moles on their right arm had approximately nine times the risk of having more than 100 moles altogether, compared to women with less (OR: 9.38, 95% CI: 6.71-13.11).

How did the researchers interpret the results?

The researchers concluded that: “the ability to estimate total body naevus [mole] counts quickly by counting naevi [moles] on one arm could be a very useful tool in assessing melanoma risk in primary care”.


This twin study used a large sample of women and a small number of men to show that counting moles on the right arm can give a reasonable indication of total mole count.

It showed that having more than seven moles on your right arm predicted the presence of more than 50 moles on you entire body, and having more than 11 predicted more than 100. Having more than 50 and 100 moles were chosen to represent higher risks of developing melanoma.

The results of this study should be interpreted with caution due to several limitations:

  • This type of study can only show a potential association between two factors. It cannot show a causal link.
  • Researchers have only adjusted for some of the confounding factors, like age, height and skin type. There are several other factors that need to be taken into account when making a connection between number of moles and melanoma – for example, an individual’s exposure to sun, whether they used sunscreen regularly and hormonal changes.
  • The results of this study cannot be generalised to men or to non-Caucasian women.

If you have noticed changes in a mole, freckle or patch of skin, especially if the changes happen over a few weeks or months, see your GP.

There is little you can do about the number of moles you have, but you can actively reduce your risk of skin cancer. The best way to prevent all types of skin cancer is to avoid sun overexposure.

Generally, using high-SPF sunscreen is a good preventive measure. The use of UV sunlamps and sunbeds is not recommended – fake tan is much safer.

You also need to be alert for any new moles or changes to those you already have.

Source: NHS UK

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