Can photodynamic therapy work on the scalp?

There are many scalp conditions that can be treated with PDT (Photo Dynamic Therapy) but the 1st thing is to identify the condition. Only then, anyone can suggest treatments.

Photodynamic therapy is FDA approved for treatment of precancers or actinic keratoses. They often occur on the scalp in men with hair loss or thinning hair. PDT is very effective treatment for this. 

Yes it can - however only for solar keratosis. There have been one or two reports for a condition known as erosive pustular dermatosis of the scalp, but there are other better treatments for this condition. I think a diagnosis of what you are treating is important. Another important thing to consider is that if you have thick hair, light ( Blue or Red) will not penetrate to the scalp, activating the ALA used in photodynamic therapy. Dr Davin Lim Laser Dermatologist BRISBANE