Yes, they can. I am currently suffering from one under both armpits as I type. It has been a little over a week, with some relief from some OTC treatments and I attest to the fact that this is a very stubborn infection to get rid of. I have read a lot of good advice here, and now believe there is hope that this will heal soon with patience and consistency. This infection has truly bought me to tears on more than one occasion, as I also did not know this type of yeast infection could occur.