Naevi are visible birthmarks or chronic lesions of skin and mucosa. These circumscribed moles can lead to the development of melanoma. But, the number of naevi change with the aging process. So, their biological understanding is vital. This knowledge will also reveal more about the genetic and environmental factors. This study relates the naevus count on different body sites with aging.

Melanocytic naevi are the strongest risk factor for skin cancer, and this longitudinal study aims to associate the naevus count and participants’ age. The researchers collected the total body naevus counts of adult twins from the TwinsUK registry (n=414). The participants’ body count got collected in a 15-year interval. The changes in the naevus number from the first and second visits for specific body sites and total body got estimated. A two-level (subject, twin pairs) negative binomial hierarchical model was the primary tool. Researchers adjusted it for age, height, skin type, and calendar year of the first visit.

The participants’ average age on the first and second visits was 46 and 63 years. The mean age difference between visits was 17 years. The naevus count increased in 235 or 57% participants, decreasing in 40% or 166 subjects. The mean difference in naevus count between two visits was 9. The total body count on the logarithmic scale increased by 0.28. Whereas, the incidence rate of total naevus count changed by 32%. The increase over time was restrictive to upper body parts only. The lower parts showed no changes.

The naevus count increased over time with age, but it was restrictive to specific body sites. This study does not confirm the overall decrease reported by previous cross-sectional studies.