Mary, what kind of nebulizer and mask are you using?
Is it a "handheld" mist type? Many of the handheld nebulizers available inexpensively are not suitable for daily use because they lack the ability to be sterilized.

Or is it the more "traditional style with a separate compressor, with tubing to deliver the air and a cup to hold the nebuluzer solution? Most people use a mouthpiece for their lung therapy, and the reuseable ones are designed to withstand sterilization. The reuseable silicone masks we used to use when our grandsons were tiny were okay in the baby bottle sterilizer as well.
Sue