Liaison office of Grand Ayatullah Sayyid Ali Al Sistani (L.M.H.L) in London, Europe, North and South America.
The ṯawāf is not valid if the body or the clothes are impure. The exceptions that are tolerated during prayer, e.g. a bloodstain that is not bigger than one Dirham (which is approximately equivalent to a 2 Euro coin), are, as a precautionary measure, not excused in the case of the ṯawāf. During the ṯawāf, there are no objections to a pilgrim carrying with them something, which is impure (nağis).
#297: During the ṯawāf, there is no objection to blood coming out of a wound, which has not yet healed, or out of an abscess if the purification is difficult to do. If not, as a precaution, the wound should be cleaned. The same applies to any kind of impurity, which cannot be removed, coming into contact with the body or the clothes.
#298: If a pilgrim was unaware of an impurity of the body or the clothes and they perceive it after completing the ṯawāf, the ṯawāf is valid and does not need to be repeated. The same applies to the prayer of the ṯawāf. The prayer is also valid if the pilgrim suspects an impurity and looks for it in vain, but then after the prayer they find it. If someone is in doubt but does not investigate and after the prayer discovers the impurity, they have to repeat the prayer as a precaution.
#299: If a pilgrim forgets about an impurity on their body or on their clothes and then recalls it after completing the ṯawāf, it is evident that the ṯawāf is valid, although it would be better to repeat it as a precautionary measure. However, if they recollect it after finishing the prayer, as a precaution, they have to repeat the prayer if it happened out of carelessness. Otherwise, there is no need for a repetition.
#300: If a pilgrim becomes aware of an impurity of their body or their clothes while performing the ṯawāf, they should remove it or change their clothes if this is possible without breaking the rules of ṯawāf, and then they should continue with the ṯawāf. If they were not able to do so, they should finish the ṯawāf and then, as a precautionary measure, they should repeat it if they perceived the impurity before completing the fourth round, although it is apparent that the repetition is really not necessary.