On a bedikah or moch dachuk, the leniency for stains smaller than a gris does not apply. Even a very small amount of red can invalidate a bedikah or moch dachuk, requiring you to start the process again with a new hefsek taharah.

However, if you suspect you have a cut or irritation that led to the red mark, or if there might have been a foreign body on the cloth, you should have the cloth evaluated before assuming you need to make a new hefsek taharah.

Please write back with any further questions.