Why doesn't my perfume smell like it used to?
Reformulation: the formula changed
Brands sometimes change a perfume's formula: because an ingredient was restricted (IFRA rules sharply limited oakmoss, which is why many classic chypres changed), because a natural material became expensive or scarce, or to cut costs. They rarely announce it. So if the new bottle of your favourite feels different, you're probably not imagining it.
Batches differ
Natural materials like rose or bergamot vary a little from harvest to harvest, so two batches of the same perfume can differ slightly. Usually it's subtle, but sometimes you notice.
A fresh bottle or an old one
Some people find a freshly opened bottle sharper on alcohol, softening after a few weeks. The reverse happens too: a bottle left half empty for years slowly loses its top notes.
Poor storage
Heat, direct sunlight and big temperature swings spoil perfume. Signs: a sour or harsh smell, a darker colour, and lost top notes. Keep bottles in a cool, dark cupboard or drawer, not the bathroom or the car. Stored well, most perfumes keep for years.
Your nose got used to it
Wear the same perfume every day and your brain learns to tune it out (olfactory fatigue). You stop smelling it, but others still do. So don't spray more to compensate! Switch to another scent for a few days, then come back. Some people also barely smell certain molecules at all, like some musks or Iso E Super.
Skin and weather
Dry skin holds perfume less well; an unscented lotion first helps. Hot, humid weather makes a scent louder and cold weather makes it quieter.
Maybe it isn't genuine
If you bought from a new place or at an odd price, it may not be genuine. See the signs in the original-vs-fake guide.