What happens if filler is accidentally injected into a blood vessel?

It’s a problem, and once that needs to be dealt with at once. If there’s a blob of filler in a tiny blood vessel, it may block it, which is bad enough – the area will look blanched, and it will be painful, and an expert practitioner will spot this straight away and will quickly inject the blockage with a substance that dissolves the filler. If it’s not treated, it may just look like a bruise but the skin tissue in the area will be dying, so it’s an emergency. If the filler gets into an artery where it can travel up towards the eye, it could cause blindness, so that is obviously an emergency, too.  Practitioners are taught to ‘aspirate’ when injecting – to pull back on the syringe once they have placed their needle into the skin, just to check that they’re not in a blood vessel, though plenty of practitioners have told me this is not completely failsafe. So it is really crucial that before your practitioner starts injecting you, you know that they have the skill and experience to spot a complication like this if it arises, and know how to handle it.