What is this yellow substance and should I remove it?

Thank you for your question. Can you post a photograph of the wound.  Your Mohs surgeon should provide you with verbal and written instructions on wound care.  Your wound may have dehisced or it may be granulating.  It is also possible that there is an infection.  An in person consultation with your Mohs surgeon is essential to make the correct diagnosis and inform you of the wound care plan going forward.  This will result in the most favorable scar.  I hope this helps.

I assume, from your explanation, that you had a partial closure of your forehead Mohs surgery wound. Having staples, which should not be used on the face, and stitches removed after ten days will likely leave suture and staple marks, which is unfortunate. The "yellow substance" is serous drainage from the healing wound. This should be cleaned out on a daily or twice daily basis or it can make the wound painful and delay the healing process. When allowing wounds to heal by second intention, my patients are instructed to clean out all yellowish material using  sterile normal saline and cotton-tipped applicators. The wound will then heal from the bottom up by filling the wound with granulation tissue. This is healing tissue very rich in blood vessels to the extent that it resembles watermelon. When this has reached the surface, my patients are instructed to stop all rubbing and begin just blotting the wound so as not to disrupt new skin coming from the outside in to cover and contract the wound. Your wound is now probably depressed and the serous drainage has solidified, making cleaning it out almost impossible. In order to allow the wound to heal normally, this solidified center of the wound should probably be excised under local anesthesia and allowed to "re-heal" as I described above. It is rare for a nickel-sized hole to take as long as six weeks to heal. For more info, feel free to contact me through real self.       jlr