Photodynamic therapy for acne also has the potential for recurrence. Acne is a chronic inflammatory skin disease occurring in the sebaceous glands of the hair follicles of the skin. The etiology of the disease is still not completely clear, and it is usually related to genetics, androgens, keratinization of the sebaceous glands of the hair follicles, Propionibacterium acnes, and immuno-inflammation, etc. If these etiological factors cannot be completely removed, then it will easily lead to the recurrence of acne. Generally, androgen level rises during puberty, which promotes the secretion of large amounts of sebum, and the hair follicles within the sebum provide a suitable environment for the growth of Propionibacterium acnes, thus stimulating the proliferation of keratinocytes at the follicular ducts and over-keratinization, which obstructs the excretion of sebum, and the sebum and keratin plugs pile up in the mouths of the hair follicles, thus forming pimples. Photodynamic therapy involves the accumulation of photosensitizers in diseased tissues, which are excited by light irradiation at specific wavelengths, producing singlet oxygen or other free radicals and causing necrosis of the diseased tissue. Photodynamic therapy is used as an adjunctive treatment for acne and does not have the effect of eradicating acne, so it is possible for acne to recur after photodynamic therapy. Patients are advised to keep their mood relaxed, avoid eating spicy, stimulating or greasy sweets, avoid staying up late, and keep the skin clean and hygienic to avoid clogging the pores with dirt, which will in turn minimize the recurrence of acne.