The laws of niddah, and particularly the decree about stains, are closely associated with the laws of ritual impurity (tumah v’taharah). Accordingly, our Sages ruled that a stain would have halachic significance only if it could render the object on which it was found ritually impure. Thus, a stain found on an object that is not susceptible to ritual impurity (e.g., a plastic chair or toilet seat, or on the floor) does not render a woman niddah or invalidate the clean days.
Regarding stains found on a white garment made from synthetic fabric, we follow the view that fabrics that are 100% nylon or polyester are not susceptible to ritual impurity. There is halachic room in some cases to treat blends with over 50% synthetic material the same way. Rayon and viscose, however, are derived from plants, so we generally consider them to be susceptible to impurity. (Note that underwear made from synthetic fabric may have a crotch made from natural fabric.)
Our site follows the halachic ruling that disposable pantiliners and pads are not susceptible to ritual impurity, so that a stain found even on a white disposable pantiliner or pad does not make a woman niddah or invalidate the clean days.
During the clean days, a woman with chronic staining may sometimes receive halachic advice to use a white pantiliner in order to avoid staining questions.
Outside of the clean days, a woman may opt to use a colored pantiliner, which provides even more ground for leniency.
According to many authorities, a stain on toilet paper, a toilet seat or toilet water is treated as a stain on an object that is not susceptible to ritual impurity. But if blood is found on any of these within seconds of urinating, the leniencies of stains may not apply. Please see our article Toilet Paper for more information.
