Can extreme temperature mess with your cosmetics?

It is true that extreme heat can affect cosmetic products but I doubt your local heat wave is hot enough or long lasting enough to cause a problem for products that you’ve purchased. Here’s why: 

Cosmetics are typically tested to ensure that they remain stable at elevated temperatures. The “torture test” is to put a product in an oven at 54C (130F) for a few weeks. Longer term testing is done at 45C (113F) for 3months and 37C (99F) for 6 months. Every company has their own test design but the end result is the same – products are evaluated to see how they react when the heat is on. 

Unless your heat wave is exposing your products to temperatures above 100F for months at a time I don’t think you need to worry much. It’s more likely that the product was exposed to high temp BEFORE you bought it by sitting in an unairconditioned warehouse or in the back of a truck.   

Of course the product type makes a difference as well. The oils used in fragrances can be very heat sensitive. Creams and lotions can separate after being stored at high temperatures for long periods of time. But heat won’t have much effect on solid products like bar soap or eye shadow. Here’s a list of products roughly ranked from most heat sensitive to least heat sensitive:

Perfume

Creams and lotions

“Creamy” shampoos,  body washes, face cleansers and liquid foundations.

Lipsticks and eye liner pencils

Mascaras

Clear shampoos and body washes 

Creamy cake makeup

Solid makeup (pressed powders)

Deodorants/antiperspirants

Bar soap

One final note: Since a bottle of perfume lasts a long time and since the ingredients are heat sensitive (and light sensitive too) that’s the one type of product that you might want to keep in the fridge.