How long does filler last?
Anon, Riverhead.
Dermal filler is an injectable gel made of hyaluronic acid. Every gel on the market varies in terms of firmness and in general, the firmer the filler, the longer it lasts.
Filler selection is based on how well it mimics tissues, whether that be skin, fat or bone. Firmer fillers are usually injected deep onto bone and tend to last up to 1-2 years on average based on manufacturer information.  Softer fillers such as the sort that is typically injected into lips and wrinkles tend to last 6-12 months as they are metabolized quicker by our tissues.
Recent MRI (Magnetic Resonance Imaging) studies have shown filler can last much longer, up to 8 years, possibly longer. This has created quite the stir on social media.  Many injectors have claimed this is a bad and scary thing; even going as far as to say they will not inject filler anymore. This is bogus in my opinion, as the product itself is inert and mimics naturally occurring hyaluronic acid we have in our tissues, so is safe to remain for years, unless there is a complication. Thankfully complications are rare and minimised by appropriate patient selection and precise sterile injecting technique at the outset, so it is always best to choose your injector wisely.
The trendy concern regarding longevity of filler is often aimed at people who look progressively odd, where filler on top of filler is administered over many years without a good objective eye keeping everything looking natural. This is crucial, as there are many instances where filler may no longer serve us, the tear trough (under eye area) a classic example, where under eye bags become puffier over time. The wonderful thing about hyaluronic acid filler however, is that it can be dissolved.
Regular clinical photography and a good, sensible eye are imperative to prevent the slow deterioration of one's appearance, often coined "Boiled Frog Syndrome."  This phenomenon is where one is treated with multiple treatments over time just as a frog tolerates slow heating in a pot. When the pot boils, the frog does not realise how hot it is and dies, much like the natural appearance of someone who falls victim to too much filler. On the contrary, if a frog is placed into a pot of boiling water at the outset it quickly jumps out, just as one should stop and correct unnatural results that can only be seen with a keen, objective eye. This is sadly variable amongst injectors, but a great rule of thumb is if your injector looks a bit puffy or odd, you probably will too.