Simple answer, NO!
"But a make up artist today said they also re-packaged Lancome, as L'Oreal."
This may come as a bit of a shocker but some make up artists do talk rubbish! (Not me, of course!
)
Large multinational corporations buy up independent cosmetics companies, like MAC, to the Body Shop for example. They do this to make money for themselves, it is their one and only motivation for doing this. They do not do it so that people who can't afford to pay for fancy packaging can have a shot at using their quality products too for a fraction of the price. Why would the do that? It's nonsense! Also, having worked for a Lauder brand myself, and therefore having a lot of their various brands in my kit (which is VERY large, so I have plenty to compare!) I can categorically say that none of the equivalent products from each brand are comparable to one another at all. My Clinique lipsticks are very different from my MAC ones, and the Lauder ones different still - as an example. This is because they are not all the same products packaged differently. I have bought Body Shop products to see what they were like, and they do not compare in any way, shape or form to Lancome. Neither do any of the L'Oreal products I've tried. You may find they use some of the same perfumes in the products, or replicate some of the shapes (ie. Bourjois eyeshadows looking and smelling similar to Chanel) - they are not daft, they are appealing to the emotional side of consumers who subscribe to these very rumours!
There is probably some crossover with R&D to a point because it would make sense to share knowledge, but they wouldn't be using the same quality ingredients in the cheaper equivalents.
Yes, some cheaper products to just as good a job as some more expensive products, and vice versa. Also what works for one person doesn't for another. It's very subjective.
MUAs are in a position to be able to use a lot of cheaper products, especially pigment based products like lipsticks because we touch up the make up frequently throughout the shoot so it doesn't matter so much if things wear off more quickly or feather, or whatever.
"OMG throw it out!"
"No,I won't thanks it's fine"
This made me pmsl too. Yes, it is fine. Products which are emolient or liquid based will breed bacteria, so foundations, mascaras, gel eyeliners, eye pencils, lipsticks etc shouldn't be kept for that long. I would use your nose, eyes and common sense to determine what this period is rather than a specific time frame. Dry, powder based products do not breed bacteria but bacteria can be present on the surface, so if you are concerned about this just get some ispropyl alcohol and wipe the surface from time to time. That will get rid of any bacteria. It's a good idea to do this with concealers and the like too to keep bacteria at bay in the shorter term.