Hi, since 3 months from winters,I have been observing a black patch type in lower lip of my son. I physically touched and checked, he didn't get any sensation or pain while rubbing or pressing. Earlier his lips are normal in colour. I thought it may be some blood clot but it's not going it's own. I hardly remember he got hurt in his lips. Pl let me know what is to be done for it's healing. Also, I have attached his photo for reference.