Abstract: The present invention relates to photosensitizer compounds for use in cosmetic and therapeutic applications of photodynamic therapy. The compounds of the present invention are designed for topical application and are characterized by a low permeability to the stratum corneum (the outer skin layer of an individual) and/or a low allergenic potential. Surprisingly, such compounds have beneficial properties in the treatment of certain diseases and lack the undesired damages to healthy skin entailed by prior art compounds. ALA (5-aminolevulinic acid)-esters of body-owned, natural compound such as aminoacids, steroids, carbohydrates, alcohols are preferred examples of photosensitizers of the present invention. The compounds of the present invention are used in the treatment of skin diseases such as psoriasis, sebaceous glands related conditions including acne, seborrhoic dermatitis, rosacea, skin cancer and precancer, as well as in cosmetic hair removal.