Yellow discharge almost four weeks post breast reduction surgery, what should I do? (photos)

This might be a slight infection. I would recommend you to meet the plastic surgeon who has operated you. He/She will be able to guide you in how to treat that. It should not be too much of a worry. It does not look too bad. So don’t worry!

Overall your wounds look excellent and you have minimal redness.  This may just be a small area of wound breakdown, an area of underlying fat necrosis, a stitch abscess or from some other cause that is hard to tell from your photos.  Clean the area with saline, cetrimide or betadine and make an appointment to see your surgeon.  It doesn't look like too much to worry about, but worth getting checked in person.

Hi There,
I understand that it has been four weeks post breast reduction. Please see you GP and make sure that it is not pus but liquified fat. This can be done by sending the fluid for culture.