SUMMARYIsolutrol is the active principle isolated from aqueous tissue extracts of deep sea shark liver and gall‐bladder. A previous study has demonstrated the ability of isolutrol to reduce hyperseborrhoea, which provides a rationale for its use in the treatment of acne. We have performed a double‐blind clinical trial on 70 patients to evaluate the efficacy and skin tolerance of isolutrol 0.15 g/100 mL (Ketsugo) in the treatment of mild to moderate acne when compared with 5% benzoyl peroxide lotion. The results from this study showed that both isolutrol and benzoyl peroxide significantly improved patients' acne by reducing the number of inflamed lesions. Isolutrol did not significantly reduce the numbers of non‐inflamed lesions whereas benzoyl peroxide did. Fewer side effects were experienced by patients treated with isolutrol when compared with benzoyl peroxide. These results indicate that isolutrol may be a useful adjunct in the treatment of acne, particularly in patients with inflamed le