Bowen's disease (BD) is a form of intraepidermal (in situ) squamous cell carcinoma (SCC) originally described in 1912.1 It presents as a gradually enlarging, well-demarcated erythematous plaque with an irregular border and surface crusting or scaling.2 BD is the frequent precancerous skin lesion in Caucasians.3 In the UK, BD occurrence is most common among patients in their 70s and in women (70-85%), and the majority (60-85%) of cases involve lesions of the lower leg.4,5 BD is estimated to evolve into invasive SCC in 3-5% of cases; therefore, treatment is recommended.6 Current guidelines suggest that the available therapeutic options (including cryotherapy, curettage, excision, topical 5-fluorouracil, and topical imiquimod) are broadly similar in efficacy, with 12-month recurrence rates of approximately 5-10%.7 However, cryotherapy can be painful, making treatment of multiple lesions difficult, and healing can be slow.8 Additionally, topical treatment with 5-fluorouracil or imiquimod is relatively slow and typically causes local irritation.9,10 Photodynamic therapy (PDT) with methyl aminolaevulinate (MAL) is an attractive treatment option for BD with large or multiple patches, and poor healing sites can be treated with good efficacy, low recurrence rates, and good cosmetic outcomes.7 PDT requires light activation of a photosensitizer in the presence of oxygen, which generates reactive oxygen species leading to selective and highly localized destruction of abnormal cells.11,12 MAL is an efficient photosensitizer, with deep lesion penetration resulting from enhanced lipophilicity. Compared to 5-aminolevulinic acid, MAL also has a greater specificity for neoplastic cells.13-15 Because histologic features of BD include full-thickness keratinocyte atypia with disordered maturation, it is typically treated twice within an interval of 1 week.16,17 So, complementary techniques are needed to enhance the penetration and accumulation of MAL in order to improve PDT efficacy and decrease treatment duration.