Unlike popular belief, candles can expire and get spoilt! Although, in certain cases, the same may simply degrade and lose their actual quality.
Scent degradation is common to all forms of scented candles and the same can lose their actual scent or may simply weaken over a period. This often happens if you have not sealed these candles properly. So, pillar candles or tapered ones that are set for display will surely lose its scent faster than any other one.
So, no matter what type of wax you use, candles may also spoil if the scent was derived using essential oils that are plant-based. The same is also true for colouring. The dyed waxes may lose their colour on exposure to UV light. Although, UV protection additives can slow this process but cannot overcome completely. So, whatever type of candle you may invest in, it may get spoilt after some time.