I had a breast reduction and lift 3 weeks ago. Spitting stitches causing dehiscence? (photo)

It does look as if some stitches may have come undone and caused a small dehisence.  Apply some antibiotic ointment and cover it with a bandage and then see your PS as soon as possible.  You can wet it and wash normally in the shower until then also.  You will eventually heal fine.

This needs immediate wound care instructions! I recommend Silvadene cream but best to ask your chosen operate surgeon for guidance TODAY!

Hello,
Sorry to hear that your surgical site opened up.  Rest assured, this is not uncommon, especially in larger reductions.  I would continue to wear your sports bra, and place a piece of dry guaze or absorbent pad in it because you can expect to see some clear to reddish drainage.  Make sure you get in to see your surgeon sooner than later so that they may follow this.  Often times this just requires some local wound care, and it closes up on its own over the course of just a few weeks.  If the scar appears wider there several months from now, that can be easily excised as an office procedure.  
Hope this helps!
Best of luck to you. 

This is very common and of no long term concern.  Keep a dry dressing in place with a comfortable bra, use soap and water daily, and be patient.  This will heal perfectly and you will have a great result.