Topical aminolaevulinic acid-photodynamic therapy for the treatment of acne vulgaris: a study of clinical efficacy and mechanism of action. - Pollock, B.; Turner, D.; Stringer, M. R.; Bojar, R. A.; Goulden, V.; Stables, G. I.; Cunliffe, W. J. (British Journal of Dermatology, 2004)