Q: Is it permissible for the pilgrim in ihram to wear a mask/respirator?

A: In cases of necessity, there is nothing wrong with the pilgrim in ihram wearing a mask, such as if he has an allergy in his nose and he needs to wear a mask, or if he is passing through thick smoke and needs to wear a mask, or he is passing by a smell and needs to wear a mask. There is nothing wrong with that.

[Sheikh Ibn Uthaymeen, Majmoo' al-Fataawa, 22/130, pg. 131]