Fit and seal check: facial hair, size and the user seal check

Two people can wear the same respirator and get very different protection, because the gaps around the edge decide how much air bypasses the filter. This sheet covers why the seal matters, how facial hair and size change it, the difference between a fit test and a user seal check, and the steps for the check itself. It is general information, and your own clinician or occupational-health adviser has the final word.

Why the seal matters

The NIOSH guide to wearing a filtering facepiece respirator (an undated page, opened 11 October 2026) puts it plainly: these respirators must form a seal to the face, and your breath must pass through the material and not around its edges. Air takes the easiest path, so a small gap can matter more than a good filter. The mechanics are set out in how masks and respirators work.

A filtering facepiece respirator is the disposable type where the mask body is itself the filter. Respirators with replaceable cartridges or canisters, also covered by OSHA's seal check procedure, rely on the same idea. For the main types, see types of masks and respirators.

Facial hair and other causes of gaps

As at 2 November 2017, a NIOSH Science Blog post reported that facial hair along the sealing area is a common reason someone cannot be fit tested, and that hair under the seal can cause 20 to 1000 times more leakage than a clean-shaven face. The same post says a loose-fitting powered air-purifying respirator (a unit with a blower and a hood or loose facepiece) may be an option when facial hair is present, after talking to the workplace respiratory protection program manager.

The HSE fit testing basics page, last updated 8 April 2025, makes the same point about stubble and beards, and adds that where a beard is worn for good reasons such as religious ones, equipment that does not rely on a tight face fit is an alternative.

Hair is not the only cause. As at 12 March 2025, CDC's N95 page lists jewelry, glasses and facial hair, and says gaps can also occur if the respirator is too big, too small or put on incorrectly. Glasses are covered in masks with glasses and hearing aids.

Fit test versus user seal check

A fit test checks whether a particular make, model and size of tight-fitting respirator suits your face. A user seal check is a quick test you do yourself every time you put one on. They answer different questions, and the check does not replace the test.

HSE says one type or size is unlikely to fit everyone, and that the test should be done by a competent person. It adds that anyone who wears more than one type of tight-fitting facepiece should be tested on each type. The NIOSH FFR guide calls fit testing the best way to confirm a respirator fits you.

When the workplace rules apply

If a respirator is required at work, the rules are stricter than for personal use. In the US, OSHA standard 1910.134 (amendment history shown to 26 September 2019) requires the employer to provide a medical evaluation before fit testing or workplace use. It also requires a fit test before first use and at least annually, with another after changes such as facial scarring, dental changes or an obvious change in body weight. It forbids tight-fitting respirators where facial hair comes between the sealing surface and the face, and requires a user seal check each time the respirator is put on.

HSE, as at April 2025, describes fit testing as something done by a competent person so wearers can choose from adequate models. A workplace respirator therefore needs a workplace programme, with a medical evaluation and a fit test, wherever the cited bodies say so. Off the job, CDC advises that anyone with heart or lung problems talk to a doctor before using an N95.

How to do a user seal check

For a disposable respirator, the NIOSH FFR guide and CDC describe two versions. Do one of them after putting the respirator on and shaping the nosepiece (the bendable strip at the top).

1. Put the respirator on following the maker's instructions, then press down on both sides of the nosepiece with your fingertips so it moulds to your nose.
2. For the positive pressure check, gently place both hands over the respirator and breathe out. If air leaks from the edges, or glasses fog, it is not snug.
3. For the negative pressure check, cover the respirator with your hands, breathe in sharply, and block the paths where air could enter. A well-sealed facepiece collapses slightly. If it does not, or you feel air leaking, it is not snug.
4. If either check fails, adjust the straps and nosepiece and repeat. If you cannot get a tight seal, CDC says to try a different size or style.

NIOSH notes that not every respirator can be checked this way, so follow the maker's instructions for your model. For respirators with cartridges, OSHA appendix B-1 (an undated page, citing a 1998 amendment) describes the same two ideas: building slight pressure inside the facepiece when exhaling with the exhalation valve closed, and a slight collapse when inhaling with the filter inlets covered, holding the breath for ten seconds.

CDC adds that even without a perfect seal an N95 likely protects better than a cloth mask. Sealing it properly is still the goal. Putting on and removing it correctly is covered in putting on and taking off a mask.

The short version

The seal decides how much of the air you breathe has been filtered. Facial hair, size and a poor fit all open gaps, and a user seal check each time you put a respirator on is how you catch them. Workplace use needs a medical evaluation and a fit test where OSHA, HSE or NIOSH say so.