According to binding rabbinic decree, an item is also a chatzitzah if it meets only one of the criteria – either rov or makpid. Thus, an item that covers a small portion of the body but is undesired, or that covers the majority even if desired, is a chatzitzah. When calculating the majority, the hair is considered a separate unit. Thus, an item that covers most of the hair is a chatzitzah, even if the rest of the body is not involved.
It would appear that hair dye, which covers a majority of the hair, could present a problem of chatzitzah. In practice, there are several reasons for leniency:
- If a woman clearly wishes an item to be present for cosmetic reasons, then in some cases it may not be considered a chatzitzah.
- Items permanently attached to the body are considered subordinate to the body, and thus are no longer chatzitzot. Therefore, permanent dyes, which stay in the hair through multiple washings, are less problematic than temporary dyes.
- There is room for leniency if an item has no independent substance (it is absorbed into the skin or hair and cannot be felt above its surface). Thus, while efforts should be made to remove unwanted ink and dye stains prior to immersion, if they cannot be removed they are not chatzitzot.
A woman wants the dye for cosmetic reasons, it is permanently absorbed into her hair, and it has no independent substance. Therefore, it is permissible to immerse in the mikveh with dyed hair.
Timing of the hair treatment does raise some practical issues. Women want the dye to be present on the hair, but not on the scalp. Therefore, dye which remains on the scalp immediately after treatment could be a chatzitzah. Dyeing appointments should therefore be scheduled long enough before mikveh for the extra dye to be removed.
On the other hand, the woman's preference for dyed hair is an essential factor in determining that the dye is not a chatzitzah. Therefore, the dye must be well enough maintained for her to feel comfortable being seen in this condition. If the roots have grown out to the point that she would not want to be seen this way in public, the dye is considered chatzitzah. Therefore, if she is planning to stop dyeing her hair, she should use temporary dyes until her hair has grown out to the point that it can be cut and left in a manner with which she is comfortable.