The answer is: Yes they do! Unfortunately, it seems like a waste, but fortunately you can finally try a new shade! How long does a lipgloss last? They cosmetic companies will say about 9months. But I think 1yr is more like it.
I just know that mascara lasts 3 months after you open it & probably 1yr unopened. Foundation 1yr after opening & 3yrs unopened.
Lipgloss I predict 1yr when opened & 3yrs. Actually it depends on what kind of lipgloss. If it's the more solid type like lipbalm then it'll last longer b/c it contains less moisture than the more creamy ones. The best guess is to just smell it & look at the colour. If it smells bad & different from when you got it, then toss it out! Same thing if the colour changes.
Cargo makes a lipgloss that contains a little strip which you put inside the tube of lipgloss when you first open it. What the strip does is that it will gradually change to a red colour through time which is around 9 months letting you know that it's about time to trash it! You shoudl try it if you're curious & especially if you have a bad sense of time or memory of when you got stuff. Even I may try it just for fun!
I personally still have a few lipglosses that are more than 2yrs old & the colour nor smell have not changed especially the more expensive ones. If you're worried about bacteria, but still want to use it I would recommend heating it in the microwave, not inside the tube. Some lipglosses already come w/ a small jar & you can heat it on low heat for around 20secs or so depending on how large the jar of lipgloss is. If you have lipgloss in a tube, then just pour it out into a small jar container or contact lens case or anything similar, you could even just pour it into a microwave dish if you want to. After you heat it, the lipgloss will turn into liquid form & then you just let it cool down a little, then you can even put it in the fridge for it to turn solid faster.
You can also make lipgloss w/ old lipsticks & those last little bits of lipliner left. All you have to do is crush it up & mix it w/ a bit of petrolium jelly & pour it into a little microwavable dish, heat it up & Voila! Then pour the liquid into your container of choice for the lipgloss to take form in, perhaps an old used up lipbalm/gloss container or eyecream jar.