Forgot to Remove a Dissolvable Stitch After Breast Lift?

My recommendation is to trim it or remove it.  In order for your body to dissolve a stitch, inflammation is required.  The more inflammation, the longer it takes your scar to look good.  If it is a lot of trouble to go back, don't worry, it will likely fall off without consequence.

Hard to make any clinical recommendations without photos or an exam. You are
going through an active healing process that will take months to
complete. Most plastic surgeons put
specific sutures in certain tissues for a reason. In a breast augmentation and mastopexy, most
usually close the tissue in layers to keep the tissue together and to
take tension off the wound. Deep layers are usually absorbable and the
skin sutures non absorbable that have to be taken out. Sometimes
sutures from the inside will spit out through the wound. If this is the
case you may have a little opening. This is usually OK, and will heal,
but should be seen by your plastic surgeon or whoever is covering for
him/her.  I tell my patients... No kitchen surgery, come in and we will take
a look. Please continue to inform your board certified plastic surgeon. 

I am certain that your plastic surgeon wants to hear about your stitch.  Each plastic surgeon has his or her own policy on sutures.  He or she may not have forgotten this suture, but actually plans to see you at least one more time. 

In our practice as in others, we continue to treat post breast lift patients until the suture line looks as good as it can for the patient's genetics.  I use a very special brand of tape on the suture line and see patients back every couple weeks to folllow wound healing until the wounds are no longer red. 

Once noticed most patients find these to be such a nuisance that it would best be removed. Thanks and best wishes.

As the name implies dissolvable stitches will reabsorb spontaneously.  The problem with some of these dissolvable stitches is that they can take up to 5 months to disappear completely.  Breast lifting by definition involves long incisions which require multiple stitches to close.  It is very common for some of these stitches to stick out and become bothersome.  I routinely snip these stitches at the skin surface and allow the remainder of the stitch to remain.  I am sure your surgeon will do the same and reassure you that this is a temporary inconvenience but not a serious problem.