If your CPAP mask was previously sealing well and is now starting to leak, then the cushion may be reaching the end of its life. Over time, the silicone used in most CPAP masks loses strength and becomes sloppier and less able to maintain a seal. Tightening the headgear can offset this to a degree, but eventually, this will not be sufficient.
This issue tends to happen after around nine months but can happen earlier. Replacing the cushion should solve the problem, but if the cushion alone is not replaceable, then you will need to look at buying a new mask.
For more information on solving mask leaks – check out our comprehensive guide.