leather that is moist smells. some from the leather itself, and some from the wearer that sweats so if you put your tfillin in the plastic shidel and into the tfillin beitel when it is moist, smelly bacteria will grow on it,and it eventually penetrates the batim and pasels the parshios so i f you are sweaty,don’t put your tfillin, in a place where it can’t dry out’, if you are a heavy sweater, then when your tfillin are dry completely.smear them litely with kosher olive oil, and let them dry again,some people need to do this every day, but only dry them in room temp. air,
heat can pasel the parshios/and mis/shape the batim /or exact rubiah i’ve found parshios that here mouldy and posul on a few occasions info by Eli Teitelbaum/sofer stam
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