One may use an adhesive bandage (“Band-Aid”) to protect a wound or a sensitive area from the friction caused by clothing or other objects. Even one who is bothered by a mild ailment may do so, since an adhesive bandage does not cure but merely protects (SA 328:23).
Although one may not affix an adhesive bandage to paper or the like because of the prohibition of Tofer, affixing one to the body is not prohibited, because Tofer does not apply to the human body. Besides, adhesive bandages are meant to remain on the body for only a short time.
Le-khatĥila, one should try not to attach the ends of the adhesive bandage to each other and to avoid using an adhesive bandage to keep a cloth bandage in place. This is because some maintain that these cases are rabbinically prohibited, as sticking one item to another in such a manner resembles Tofer. If necessary one may be lenient and rely on those who maintain that since adhesive bandages are affixed temporarily, for a short period of time, one may do so just as one may tie a temporary knot that lasts only a short time.
One may not cut a bandage or adhesive bandage to size, and one who does so violates the Torah prohibition of Meĥatekh (MB 322:18; above 15:10). If a bandage is too long, one should wrap it around the injury multiple times rather than cutting it. If one knows that he may need to bandage wounds on Shabbat, he should prepare bandages of various sizes before Shabbat. It is also good to prepare methods of fastening them with safety pins or an elastic sleeve, since it is preferable le-khatĥila not to use an adhesive bandage in order to keep a cloth bandage in place.
One may use a butterfly bandage to hold together the edges of a cut. This is because of two lenient opinions. First, some maintain that there is no prohibition of Tofer when it comes to the body. Second, some say that this type of bandage cannot qualify as sewing, since all it does is hold closed the edges of the cut, helping the wound close up on its own (SSK 35:25; see Harĥavot 27:2:4).
In order to stop bleeding, one may use a bandage (using a permissible method of tying) or antihemorrhagic sprays or powders (like Dermatol). These measures are not considered medicinal; they simply stop the bleeding (see SA 328:29). Additionally, one may place iodine on a wound in order to prevent infection (SSK 35:13).
One may clean blood with a bandage or paper towel, even though this will color them red. Similarly, one may bandage a wound that has been treated with iodine, even though the color of the iodine will stain the bandage or paper towel. This is because this “coloring” is in fact a manner of soiling the material. Additionally, none of these items (bandage, paper towel, body) are meant to be dyed (SAH §302, Kuntres Aĥaron; MB 303:79 and 320:58; above 18:5).
If an adhesive bandage is irritating, one may remove it. When doing so, le-khatĥila one should try to avoid ripping out hairs, because of the melakha of Gozez. If there is no alternative, one may remove the adhesive bandage even if it is clear that this will rip out hairs, since one does not want this to happen and it is simply an ancillary effect of his action (SSK 35:30).
. Orĥot Shabbat ch. 20 n. 250 expresses surprise at SSK’s permission to use Dermatol, maintaining that it is indeed medicinal. R. Shlomo Zalman Auerbach seems to maintain that Dermatol and iodine are not meant to heal, but simply to stop bleeding and prevent infection. In any case, even if they do heal, someone who is suffering would be permitted to use them, as I pointed out here in section 5 and n. 3.