Charles Ellicott Commentary Leviticus 15:23

"And if it be on the bed, or on anything whereon she sitteth, when he toucheth it, he shall be unclean until the even." — Leviticus 15:23 (ASV)

And if it is on her bed. —Better, and if any object is on her bed, that is, if anything happens to lie on her bed.

When he touches it. —Rather, if he touches it. The former two verses declare that if anyone touches the bed itself, or the thing on which she sat, he contracts such a degree of defilement that he must wash his clothes, bathe his whole body, and remain in a state of pollution until sundown. However, the verse before us enacts that if he happens to touch any vessel, garment, or any other objects lying on the defiling bed or seat in question, he only has to remain unclean until sundown, without having to wash his garments. The defilement in this case is not primary, but secondary. It is no longer the bed or seat that defiled by direct contact, but an object that the defiled bed or seat had defiled; the pollution in this case is indirect.