Just found out that if I change light on my face, hair stayed exactly the same.
I just have some black planes above my character to block the light.
The face take the shadow but not the hair.
Why does my lighting does not affect the hair ?
Worked! Thank you!
Up ! Anymore help for the reddish eyelashes problem and wrong reflection on hair ? 
(only with r.HairStrands.SkyLighting.IntegrationType 1)
I’d try increase the melanin of the hair material instead.
The only fix I have found that worked, finally, was to go into the Metahuman parent hair material graph (M_hair_v4 in my case), and make sure your SetMaterialAttributes output node is connected to the shader listed in the Feature Level Switch that you are actually using in your preview device profile in the project editor settings. I am on a Mac using SM6 and after connecting the node to SM6 all hair problems are gone. Default is ES3_1
I had this same issue, and what fixed it for me was to select all of my grooms together (hair, brows, etc.) and, under “Groom”, set “Use Cards” to true (checked). Hope this helps others!
Worked Thanks
So none of these methods worked for me. I did however find that it was the directional light causing issues. Specifically the source soft angle. Reducing this fixed the problem for me
UE 5.5 has a new cvar that greatly improves skylight occlusion:
r.HairStrands.SkyLighting.ScreenTraceOcclusion 1 combined with
r.HairStrands.SkyLighting.IntegrationType 1
Hi @The_Distiller, have you ever experienced issues with noise in hair and weird flickering caused by a backlight, like this one? I increased the light sample to 32, and I’m also using some CVRS, including the one from Epic staff here. However, it still doesn’t solve the problem. I’m wondering why this happens. Do you have any ideas? Thanks!!
In UE5.6, in the assembled metahuman blueprint, I set num LODs, Forced LODs, and Min LOD all to 0 and it seems to have improved the issue. But, of course, this means that the engine is using the highest quality MH LOD, which results in less optimization.
