Fig. 2.

Methods of increasing ALA penetration into the skin. Fractional laser, iontophoresis, penetration enhancers, and intracutaneous injection are all methods/techniques to either improve the permeability of the skin or increase the penetration ability of ALA. Fractional laser irradiates the skin to remove skin layers in microscopic holes so ALA can reach deeper structures underneath. Iontophoresis is a technique to push compounds into the body through the skin by applying a local electric current and creating a repulsion force. Penetration enhancers work in combination with ALA (usually as an emulsion of other substances) to increase the ability of ALA to move transdermally across the lipophilic stratum corneum. Intracutaneous injection is the simple approach to inject ALA into the skin