You will find it works better to select the lip faces ( I thought there was a lip texture with a mask in CC3 and 4 that would add this, perhaps in Makeup…
and then add a new material …using a greyscale Mask texture and Blending Between the Face and Lip materials.
Here is an older thread for a way I use…
P.S… At some point, perhaps in your screenshot, you mangled the UV for the eye. It is broken up into several islands…To use the Iris textures, you will need to unwrap the eye to fix it…