Photodynamic therapy using aminolaevulinic acid does not lead to clinical improvement in hidradenitis suppurativa

Sir, Hidradenitis suppurativa (HS) is a chronic, inflammatory, scarring disease of the apocrine sweat gland‐bearing skin.1 The primary event in the development of abscesses and sinus tracts is follicular occlusion caused by keratinized, stratified squamous epithelium, with the apocrine glands becoming involved only at a later stage.2 Treatment approaches are similar to those in acne vulgaris, including topical and systemic antibiotics, hormonal therapy and oral retinoids. Phototherapy with a combination of blue (415 nm) and red (660 nm) light was found significantly to reduce the number of comedones in patients with acne.3 In addition, photodynamic therapy (PDT) using aminolaevulinic acid (ALA) has been shown to be an effective treatment in acne vulgaris.4 A study by Hongcharu et al.5 has provided some evidence to support a reduction of follicular obstruction through changes in keratinocyte shedding and hyperkeratosis as a possible mechanism of action of ALA‐PDT in acne, although much higher fluences of light were used in this compared with previous studies.3