Question: Why is 311-312 nm of UVB light the most beneficial portion of light for eczema phototherapy?

Paul O'Mahoney answered on 8 Mar 2016:

Lots of things in the skin and body react differently to different wavelengths of light. This is because different wavelengths of light also carry different amounts of energy, and things such as proteins or molecules only respond to certain levels of energy – too much or too little energy won’t always work, so you need to hit your target with just the right level of energy. It so happens that using UVB light with just the right energy helps to suppress the immune cells responsible for over-production of skin and inflammation, so it is quite effective for helping with eczema