How come when a frag is from the 90s or older it always has that old school smell to it? Was it the way fragrances were made back in the day that has changed or the perfumers taste that changed over time?
If you are smelling the fragrances in their vintage formulations I believe you are indeed most likely sniffing some of those rarely used raw materials nowadays due to cost, scarcity and/or IFRA restrictions as L'eaulita indicated in her prior post.
For example, a commonly used key ingredient back then, oakmoss, has all but been shelved from a usability perspective in current compositions and has forced re-formulations of many classics due to IFRA restrictions on the amount of the ingredient that can be used. As a result most of the magic those classic fragrances once had in their original vintage formulas has been sucked away and many that remain still in production are regrettably a shadow of their former selves.
Just like anything else many of those formulas smell "old" to some of the folks nowadays because they are unaccustomed to the ingredients in them and as a result tastes have indeed changed to a degree. Of course some of the reformulated classics just no longer smell good due to the missing/changed ingredients and some folks who never sniffed the vintage releases base their opinions on the classics derived from what they smell now, having no idea what they are missing. Too bad really on all counts.
For some of the scents, the notes may also be deepening and otherwise changing over time, making an older bottle of a given scent smell very different than it did when that same bottle was first purchased. If a person were to use or sniff at that bottle somewhat regularly, it's possible that he or she wouldn't notice the scent evolving in the bottle. Then, when the bottle needs to be replaced, a new one will smell different, leading in such cases to inaccurate speculation about reformulated scents.
I'm kind of a fan of the classics both the lower priced and the higher end ones - not sure exactly why I think it may be that sense of history they provide, such as "Dietrich wore this, or Liz Taylor wore this or Errol Flynn wore this" etc and then there is that "test of time" thing - there is a reason things stick around, people like them, and people buy them, otherwise why continue to make them? Oh I know some are simply a statement of a perfumers art etc, but there are just so many and many are little unknown classics much like the pretty girl who lives in the tiny village who is known so well by the 300 or so people in her village but she has never been to the city or anywhere really so her beauty remains known only to the few - the world of scent is such a lovely and multifaceted thing.
There was apparently concern about skin reactions in combination with treemoss:
Both Oakmoss and Treemoss extracts contain chemicals that are are sensitisers and can cause contact dermatitis and allergic reactions in some people. IFRA restricted the use of these materials, allowing only a very small amount to be used in on skin fragrances. IFRA is contemplating reducing the amounts used even further,effectively making it impossible to use them.
If you could give us some examples that would help quite a bit, so let's consider some:
Kouros: urinous honey, civet, heavy musk, and a boatload of other things
Givenchy Gentleman: patchouli, honey, and worn leather
1-12: galbanum, oakmoss, etc.
various "women's" scents such as the original Armani: oakmoss and lots of aldhydes
Dali Pour Homme: castoreum
JHL: sandalwood, "dirty" jasmine
The above either have a lot more of certain ingredients than you find in recent designers or the ingredients are no longer being used; or, what's being used is a pale imitation. On the other hand, as others said, there are new molecules being used that many probably regard as "normal," such as calone, iso e super, various "laundry musks," what I call "cheapo cedar", etc. Notions of "old" suggest cultural conditioning, and a few years back I also had such perceptions. Today, to me smells have no connections. In some cases I find them really "bad" but my mind says, "terribly unbalanced," such as with human waste. My guess is that most perfumers come to that point as well.