Why is my CPAP filter black?

What would cause your CPAP filter to become black so fast? Well, besides the obvious suggestions like never cleaning it, dirty air, and age, the most common causes are things like smoking, candles, and incense.

No air is 100% clean. So it is normal that the air filters in your CPAP can become dirty. But if they are becoming black overnight, then something else is going on. Candles are a popular culprit. If you burn a candle at night while your CPAP is in use, there is a good chance a brand new filter will be black the next morning.

How can a candle turn a filter black? It is a very little known thing known as “Black Soot Deposition.”  When candle wax burns, it produces small, black soot particles that attach to things around the house, especially on walls or carpet. If a CPAP machine is running at the same time, it wont take much for those black soot particles it get grabbed by the filter.

This is more typical with scented candles. You normally won’t have much of an issue if you burn candles while the CPAP is off. So if you want to burn a scented candle in the bedroom, it might be best to do it an hour or so before bed, then blow it out before you turn your CPAP on. Another option is too use candles that don’t have a lot of chemicals for a strong smell.

I had this problem when it only took a few days for my filter to be completely black. It was odd to me, because it happened so fast and my house is more than reasonably clean. I asked my supplier where I got my machine from and asked them for advice. They questioned me about smoking, cleanliness, etc. Eventually they did ask me if I used candles at night. It didn’t take me long to answer “yes.” My girlfriend often would light a candle overnight. usually a scented one

The tech told me that is mostly likely what caused it. My girlfriend loves me, so we stopped using candles when we slept. I haven’t had any more issues with my filters becoming so dark so fast anymore.

And just like burning scented candles, smoking and burning incense can also cause black soot deposition. And again, these things would have to be happening at the same time the CPAP is running.  These things can literally turn a brand new filter black over night.

If you don’t burn candles/incense, and no one is smoking while you are sleeping, you might want to check the air quality you are in and do a deep cleaning. Excessive dirt and dust in the air is probably what is dirtying your air in this case. Using air purifiers can help clean the air in your bedroom which may not only help your filters in your CPAP, but help your over all air quality that you breath in. And air purifiers can be quite affordable, especially if you are getting it for a small bedroom.

The filters will want to maintain, replace, and clean the filters regularly to make sure they don’t build up a lot of dirt. I have the Philips Dream Station BIPAP. It has 2 filters, one thin, light blue that gets replaced every 30 days or month. And then a dark blue one which gets rinsed under water which I do every 2 weeks. I replace the big dark blue filter about every 3-4 months even though I rinse it off.

No air is 100% clean so it is important to follow the guides the manufacture recommends.  But if it is only taking a few days for your filters to get covered in black, you will want to investigate the cause and make changes. Our CPAPs are expensive, so we should take good care of them.

I wrote a pretty in depth article about cleaning and maintaining your CPAP that can give you more tips and advice


Dan was diagnosed with sleep apnea in 2017 when he was only 32 years old. He has been using a BIPAP machine for his treatment. He hopes to provide a patient's perspective on the sleep apnea experience. Dan lives in Tampa with his girlfriend and 2 dogs.

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