The lipstick index:

It’s a theory of economics that states that lipstick sales rise when the economy is in a downturn. People might skip bigger, more costly purchases but continue to indulge in little luxuries, which are cheaper, to brighten their mood or keep things normal. The term was coined by Leonard Lauder, who is the chairman of Estée Lauder, in the context of the 2001 recession.
Here’s a more detailed explanation:

The Theory:
The lipstick index relies on the premise that in times of economic stress, people continue to want small indulgences and treats, but they become more cost-conscious and instead choose lower-priced alternatives.
Affordable Indulgence:
Lipstick as a relatively low-cost luxury product does fit this category. People might view it as a means to feel good without spending a lot of money.

Correlation, not Causation:
Although the lipstick index implies that lipstick sales can keep in touch with economic recessions, it is not a flawless predictor. Lipstick sales can also be affected by trends, promotions, and seasonal buying.

Beyond Lipstick:
The idea has branched out into other “affordable luxuries” such as tiny cosmetics, perfumes, and even some food and beverages that could even experience higher sales during times of recession.