I only wear cotton masks. Lets the body breathe better.
Formaldehyde on a living person sounds creepy.
Masks tend to fit the same.

Then it’s  probably sizing which is a good reason to wash it first.

Whatever it was, was strange. I never got it from other ones I bought.

It could even be due to the size of the air holes in the weave.

Ughh!! Maske is the worst! It is because I cannot find other ways on how to prevent it. It is also not safe to go outside without wearing a mask. I think it is because of the mask rubbing on the face. Ears also hurt because of the rubber thingy. Any suggestions how to avoid maskne? 

I have masks that are too big, so I fit them to my face.  See if you can get larger ones that won’t rub, or find the type with elastic that goes over the back of your head rather than your ears.

Yes, it could. I have 6 and all are cotton. I wore others of the same brand at Fred Meyer, fresh out of the package, but not all day. They all got washed by hand when I took a bath the same night. Later, I have worn the washed ones all day.

See if pony tail elastic sold in the comb and brush dept would work or go to a fabric store and buy elastic there.

I need to wash and refurbish all of my cotton ones.

Everyone does.I wonder how often any if them are washed after using?