If there is even the tiniest amount of ḥayḍ blood on the body or clothing of someone performing prayers, the prayers are invalid. Furthermore, based on obligatory precaution, the same applies with regard to blood from an intrinsic impurity (ʿayn al‑najāsah) – such as a pig or a corpse – and blood from an animal whose meat is unlawful to eat, the blood of lochia (nifās), and the blood of an irregular blood discharge (istiḥāḍah).
However, there is no problem in performing prayers if there are other types of blood on one’s body or clothing – such as blood from a human being or an animal whose meat is lawful to eat – even if it is on a number of areas of the body or clothing, provided that their combined area is less than that of a dirham.