A couple may not touch each other during the time the wife is niddah. Furthermore, there are additional prohibitions to prevent even the possibility of touching, such as passing objects from hand to hand.
Touching and Passing
Touch – even in the most mundane circumstances – can create the desire for further physical closeness. Therefore, husband and wife may not touch each other during niddah. This applies even through clothing (e.g., one spouse cannot brush snow off the other's coat while he/she is wearing it).
There are additional prohibitions to prevent even the possibility of touching. It is prohibited to pass objects directly from hand to hand. This rule applies not only to small items, such as keys or coins, but to large objects as well. One spouse should place the object on a handy surface, or strategically drop it, and the other should pick it up. Alternatively, a third person can act as an intermediary.
Throwing objects on a straight line directly from one spouse to the other is also prohibited for Ashkenazim. Throwing something on a trajectory (volleyball) or bouncing it (ping pong, indoor squash) is a matter of dispute among Ashkenazi halachic decisors. Sephardim permit throwing, even directly.
There are some exceptions to this rule. If a large object, such as a baby carriage, needs to be carried by two people, and the husband and wife are the only ones available, they can carry it together. The object should be between them, so that there is no possibility of their actually touching each other.
Babies and children who are old enough to reach of their own volition from one parent to the other can be passed directly if the couple are careful not to touch each other. Young infants should not be passed directly, but should be placed momentarily on a seat, in a stroller, etc., or handed to a third person. If this cannot be done safely, the baby may be transferred directly, with the parents being careful not to touch each other. It is permissible for the husband to place the baby on his wife's bed while she is lying there (or vice versa).
According to Ashkenazi custom, a couple may not sit together on the same seat if it is moving (e.g., a swing), or if the weight of one person will be felt by the other (e.g., a soft couch), unless there is an object or another person between them. Many Sephardic authorities are lenient in this area and allow a couple to sit together if they can avoid touching.