Does henna prevent water from reaching the hair?

Question : And what is your opinion? Yes, regarding henna, if it is applied to the hair, does it prevent water from reaching the hair?

Answer : Yes, if henna is applied to the hair in a thick layer, it prevents water from reaching it. However, in wudu (ablution), there is no harm in a woman wiping over it. But in ghusl (full ritual bath) for janabah (major ritual impurity) or hayd (menstruation), this henna on the head must be removed so that water reaches the hair. This is because ghusl for janabah does not allow wiping over anything except a cast, which is a bandage placed on a wound or nerves out of necessity; this may be wiped over in janabah and minor ritual impurity. In summary, even though henna prevents water from reaching the hair, it is permissible in minor ritual impurity, i.e., in wudu; a woman may wipe over her head even if it has henna on it. However, if there is a ghusl for janabah, hayd, or nifas (post-natal bleeding), she is required to remove it so that water reaches the roots of the hair.