A method and formulation for the delivery of an active substance to the skin (epidermis, including the stratum corneum and viable epidermis, and dermis) of a subject. The formulation comprises oil-based or aqueous droplets comprising the active substance within a coating of nanoparticles, particularly silica nanoparticles. The active substance may be suitable for the treatment of a disease or condition which is localised, or at least partially localised, to the skin (eg skin cancer, psoriasis, eczema, infections including bacterial and fungal infections, acne, dermatitis, inflammation, and rheumatoid arthritis).
