Ståle Ramstad and colleagues at the Norwegian University of Science and Technology recognised that the bacterium Propionibacterium acnes is known to play an important role in acne and have examined the use of photodynamic therapy (PDT) to treat the skin condition.

Ramstad's research has shown that the clinical treatment of the skin with aminolevulinic acid (ALA) at high temperatures makes the bacteria especially photosensitive. ALA is a biosynthetic precursor of the porphyrin compounds, and the raised incubation temperature helps speed up their production. However, as Ramstad notes, 'the pathogenesis of acne is by no means clear.'  Despite this fact, P. acnes seems to be the main target for traditional antimicrobial treatment, but 'PDT could be beneficial by several mechanisms, not only (those directed) against P. acnes.' 

P. acnes can be seen as fluorescent spots when shone with near-UV light because the organism produces small clusters of porphyrin compounds. These compounds make the bacteria sensitive to blue and red light and the porphyrins lead to oxidation reactions and cell death. Since these porphyrin compounds are not present in the skin, and the technique does not use UV light, it is thought to be safe, and the development of resistance seems unlikely.