It could be mites. Check carefully to see if you see any you should see them.

It is often also related to humidity, hygrometers are temperamental tools and often go off. Digital units are especially suspect, they often get stuff on the micro carbon pad and basically any dust can change the reading. I have a number that have read over 30% in error. Analogue gauges are far more robust, however the cheap ones with the paper face card bind too easily, they also can be accurate but rarely stay that way.

I would suggest checking the hygrometer first (salt test for analogues and a hygrometer calibration kit, cigar stores sell them, for digital units)

Look for mites very carefully don't just treat using any chemical. P-A-M is a potent poison and has over many years killed a number of snakes due to incorrect use. I have herd of a couple of cats as well (PERMETHRIN or 3-phenoxyphenyl) is very toxic to cats. Be very careful using any poison, they demand respect. It is in the phenol family of insecticides, yet if I were to suggest spraying cedar oil all over the enclosure I am sure someone would say that is a bad idea. PAMs active ingredient is a synthetic source of a similar chemical. 25 years ago cedar was though to be beneficial, now not so much. Be very careful when using pesticides they are poison. The only EPA approval I can find on PAM aka CIC Residual Pressurized Spray No.V is under 50404-7. But that is approved only for dogs.

(http://www.epa.gov/opp00001/chem_sea...7-20110801.pdf) if there is a correct number anyone knows of I would love to see it. There seem to be few MDSD sheets on the product.

If you decide there are mites, and don't want to use a chemical treatment there are a lot of non toxic mechanical methods to kill mites, they just take some effort.