Why is my dog's spay incision red with a blister months later?

This is probably happening due to an allergic reaction to the suture material, it is quite common. these sutures usually dissolve completely within 4-6 weeks, which might be the time it will take to resolve.

The vet most likely used a suture material for the spay that takes a very long time to dissolve (like PDS) and she is having a reaction to that suture material that is still left there. I would not be worried about this unless it abscesses and opens. For now, just monitor it.

The wound appears very superficial in the picture and I would leave it open to the air without dressing. Manuka honey and saline washes once daily may help if it becomes crusted. It is possibly due to a reaction to suture material which although rare can occur (surgical repair is a last resort as healing can be slow!)

While it can take a long time for sutures to dissolve, and may cause some swelling or irritation, if the area is still very inflamed, is bothering Mikasa, you're seeing sutures actually coming out of the incision site through the skin, or the area is hot to the touch or lumpy, I'd get a second opinion from another vet. It's possible there is an ongoing reaction under the skin that needs to be addressed, or the sutures removed and the area examined to check for other causes. Until you can get to the vet, making sure to keep the area clean and dry to prevent infection, and keeping Mikasa from licking at it is best.

This could be a local tissue reaction to the internal sutures. It can happen, and it's good that it's gone down. Keep an eye on it, and if it gets bigger or doesn't go away, have Nova seen by a vet.

This looks like a reaction to the stitches that were used under the skin from the spay surgery. There is a type of suture that your vet may have used that takes months and months to completely dissolve. That is my best guess as to what is going on. I don't think you need to rush her to an ER but I do think you need to get her an exam with your vet sometime in the next 24 hours. Try to keep her as calm and quiet as possible in the meantime. Watch it carefully, if it starts to look swollen she needs to see an ER vet.

It is not uncommon for dogs to have a mild reaction to under the skin sutures. As long as there is no pain, discharge, odor, or opening of the areas with suture sticking out, it will likely resolve with time. It takes a long time for sutures to dissolve. See your vet if she is bothering the area or you notice any of the signs above. I hope this helps and thank you for using Petco Pet Education Center, formerly Petcoach!