There is a lack of good-quality evidence from randomized controlled trials (RCTs) regarding the effects of dietary interventions, hygiene measures, or exposure to sunlight. The available observational studies are inappropriately designed and of insufficient methodological quality to draw meaningful conclusions.

• A systematic review (search date: July 2003) investigated the influence of diet, washing, and exposure to sunlight, on acne [Magin et al, 2005a]. Most of the identified studies had significant methodological limitations, such as small sample size, lack of control subjects, lack of blinding, or unclear or unstated statistical methods. The authors concluded that there was insufficient evidence to draw conclusions on the efficacy or lack of efficacy of dietary and hygiene measures, or exposure to sunlight.
• Dietary factors
• Three prospective studies of very limited quality found no relationship between chocolate or sugar consumption and acne.
• An observational study found that soldiers 20–40 years of age with acne were significantly heavier than their counterparts without acne. However, more evidence is required to ascertain if this is a true causal relationship.
• One observational study found that non-Westernized people from Papua New Guinea and Paraguay did not develop acne. It was suggested this could be because of the high glycaemic index of most Western foods, although more evidence is required to support this hypothesis, and the practicality of avoiding something as generalized as a 'Western diet' is questionable.
• A correlation between worsening diet quality, and acne before exams, was noticed in an observational study (using self-assessment questionnaires), but the confounding factor of stress and the poor methodological quality of the study cast doubt on causality.
• Hygiene, washing, and use of medicated soaps
• Several studies of specific medicated soap products or washes have claimed that these products are beneficial, but the small size of these trials and lack of controls makes them hard to interpret. More rigorous studies of topical anti-acne products of known activity (see evidence on Topical antibiotics compared with placebo) suggest that there is a significant placebo response to topical treatment.
• Combined data from two controlled trials suggested that the use of chlorhexidine vehicle alone was more effective than benzoyl peroxide dissolved in chlorhexidine solution. However, this seems contradictory when compared with other studies with better methodology which found benzoyl peroxide to be an effective treatment for acne (see evidence on Benzoyl peroxide compared with placebo).
• Povidone-iodine cleanser was reported to improve acne in one RCT, but evaluation of the trial suggests that the statistical analysis was unsatisfactory. A further RCT studied various cleansers and washes, but the results cannot be interpreted due to the concomitant use of topical antibiotics.
• Exposure to sunlight
• One study in Saudi Arabia concluded that acne improved in summer months due to increased exposure to ultraviolet light. However, this should be interpreted with caution as confounding factors were not taken into account.
• Other studies on the effect of seasonal variation on acne have shown that equal numbers of people improve, worsen, or stay the same during the summer.
• Trials using artificial sources of ultraviolet light have shown slight improvements in acne, but are limited by a lack of controls or blinding.
• CKS found one further RCT. This was a small, investigator-blinded RCT (n = 43) in which people were randomized to a low glycaemic-load diet (intervention) or a traditional high glycaemic-load diet (control) for 12 weeks [Smith et al, 2007].
• There was a significant decrease in the mean total lesion count in the intervention group (–22, 95% CI –19 to –27) compared with the control group (–14, 95% CI –9 to –19; p = 0.01).
• There were also significant benefits in the intervention group in terms of body weight and some biochemical parameters (free androgen index and insulin-like growth factor binding protein).
• The authors concluded that although these results suggest that dietary modification may have an effect on acne, weight loss may have contributed to the overall treatment effect and further studies are required.