According to the American Cancer Society, more than 1 million cases of basal cell or squamous cell cancer occur annually in the US alone, and almost 2,200 Americans will die of these cancers this year.

The primary risk factor for skin cancer is excessive exposure to sunlight, particularly between the hours of 10:00 am and 4:00 pm. Repeated overexposure to this harmful ultraviolet radiation may result in solar keratosis (SKs), which consists of scaly or crusty plaques on the skin surface. SKs are dry and rough to the touch and may appear in a variety of colors. They occur most commonly on those parts of the body regularly exposed to the sun, such as the face, ears, scalp, neck, backs of hands, forearms, and lips. SKs are noncancerous skin lesions, however, if left untreated, some may progress to either squamous cell or basal skin cancer.

This week, a new study published in the April 24, 2003 issue of the Archives of Dermatology joins a growing body of scientific literature supporting the use of daily applications of sunscreen for reducing the occurrence of solar keratoses and its associated skin cancers. Daily supplementation with beta carotene , once believed to be a cancer-preventing agent, was found to have little to no effect.

About the study

This study was the intervention phase of the Nambour Skin Cancer Screening Trial, which began in 1986 and included 3,000 residents between the ages of 20 and 69 of Nambour, a township in southeast Queensland, Australia.

For this phase of the study, 1,621 adults between the ages of 25 and 74 were randomly assigned to one of four treatment groups:

  1. daily use of a broad spectrum sunscreen (water resistant with a sun protection factor of 16) plus one 30 mg tablet of beta carotene
  2. daily use of the same sunscreen, plus one placebo tablet
  3. daily 30 mg tablet of beta carotene only
  4. daily placebo tablet only

Daily use of sunscreen was defined as application of sunscreen to all exposed sites on the head, neck arms, and backs of hands every morning. Participants who were not randomized to daily sunscreen application were asked to use it at their own discretion.

The participants were examined three times between 1992 and 1996. During each examination the researchers recorded the number of SKs on 14 separate body sites.

The findings

The researchers found that while the overall number of SK lesions in the study participants increased over this time period, the ratio of SK counts in those participants randomized to daily application of sunscreen was 24 percent lower over the first two and a half years of the study than it was in those participants randomized to apply sunscreen at their own discretion. This reduction is thought to be roughly equivalent to the prevention of one SK lesion per person in the daily sunscreen group.

The 30 mg beta carotene supplement showed no significant effect on SK counts.

How does this affect you?

The study’s findings support the results of two earlier sunscreen intervention studies, which showed that daily, liberal use of sunscreen by ordinary people under normal circumstances can result in a significant reduction in their risk of developing SK, a pre-malignant skin lesion.

The researchers also found that daily application of sunscreen was significantly more effective in preventing the development of SK lesions than in promoting their regression once they have occurred. The researchers advocate regular sunscreen use as an important sun protection strategy, particularly among those who are younger or who tan easily.

Finally, the failure of beta-carotene, a vitamin supplement, to prevent SK is yet another blow to a popular anti-oxidant vitamin, which has repeatedly failed to live up its once formidable reputation as a cancer-fighting supplement.