We spend plenty of time thinking about what hot weather does to our skin — but what about the products sitting on our bathroom shelves, in our handbags or, even worse, inside a hot car?
Heat can affect your skincare and makeup too.
From melting lipsticks and separating moisturisers to changes in colour, texture and fragrance, prolonged exposure to high temperatures can alter a cosmetic product.
And if you use organic or natural beauty products, there are a few additional things worth understanding.
What actually happens to cosmetics when they get hot?
Cosmetics are carefully formulated mixtures of ingredients designed to remain stable under normal storage conditions.
Heat can upset that balance.
According to the US Food and Drug Administration (FDA), temperature changes and exposure to sunlight and air can cause cosmetics to change in colour and texture and may alter their smell. Emulsions — products containing mixtures of oil and water, such as many moisturisers and foundations — can also separate.
More importantly, the FDA warns that excessive heat can cause preservatives to break down, potentially allowing bacteria and fungi to grow more readily.
So that lipstick melting in your handbag isn't necessarily the only thing you need to worry about.
Your car may be one of the worst places for your makeup
We've probably all done it.
A lipstick gets left in the glove compartment. A makeup bag stays in the car after a day out. Your moisturiser travels around in your beach bag all afternoon.
On a hot sunny day, the temperature inside a closed car can become considerably hotter than the temperature outside.
The FDA specifically advises consumers not to leave cosmetics exposed to heat, such as inside a hot car, because heat can affect preservatives and encourage microbial growth.
So during a heatwave, take your makeup bag with you.
Which beauty products are particularly vulnerable?
Lipsticks and balms
Lipsticks contain combinations of waxes, oils, pigments and other ingredients.
Heat can soften or melt them and potentially alter their original texture. Natural and organic lip products frequently contain plant oils, butters and naturally derived waxes, making careful storage particularly sensible.
If your lipstick becomes very soft, move it somewhere cool and allow it to return gradually to its normal consistency.
Moisturisers and creams
Creams and lotions are often emulsions containing both oil and water.
Excessive heat can destabilise an emulsion, potentially resulting in separation or changes in consistency.
If a cream that was previously smooth suddenly becomes watery, lumpy or noticeably different after being exposed to extreme heat, don't simply assume that mixing it back together makes everything okay.
Serums
Serums can contain delicate botanical extracts, oils, antioxidants and other active ingredients.
Protect them from prolonged heat and direct sunlight and follow the manufacturer's storage instructions.
This is one reason you'll often see serums packaged in dark or opaque bottles — packaging can form part of the product's protection from its environment.
Mascara and liquid eye products
Be particularly careful with products used around the eyes.
Every time you use a mascara wand it can be exposed to microorganisms. The FDA notes that eye cosmetics generally have shorter usable lives than many other cosmetics.
If the consistency or smell of your mascara changes, replace it.
And never add water to dried-out mascara to revive it.
Natural oils
Plant oils aren't immune to deterioration simply because they're natural.
Heat, oxygen and light can contribute to oxidation of oils. If an oil develops a noticeably unusual or rancid smell, that's a sign you shouldn't ignore.
Perfume
Your beautiful perfume bottles may look lovely displayed in sunlight, but a cool, dark cupboard is generally a better home.
Repeated exposure to heat and direct sunlight can affect fragrance ingredients and alter the scent over time.
But what about organic cosmetics?
Here's where things become particularly interesting.
There is sometimes an assumption that organic cosmetics don't contain preservatives.
That isn't necessarily true.
Water-containing cosmetics require an appropriate preservation strategy to remain microbiologically safe. Certified organic standards recognise this.
Under the international COSMOS standard used for certified natural and organic cosmetics, only specified ingredients and processing methods are permitted, and the standard includes a restricted list of permitted preservatives.
COSMOS certification also covers far more than the organic ingredients themselves. Requirements extend to ingredient origin and processing, manufacturing, storage, packaging, environmental management, labelling and independent certification.
So certified organic means considerably more than simply putting the word “natural” on the bottle.
Organic vs conventional cosmetics in hot weather
There isn't a simple rule that says conventional cosmetics cope with heat while organic cosmetics don't.
Both can be damaged by inappropriate storage.
The difference lies more in how products are formulated and which ingredients and processing methods are permitted.
Conventional cosmetics have access to a very broad range of cosmetic ingredients and preservation systems.
Certified organic cosmetics must operate within the restrictions of their certification standard. COSMOS, for example, permits certain preservatives while restricting many petrochemical-derived ingredients and placing requirements on sourcing and processing.
That means you shouldn't assume an organic product is unstable — properly formulated certified organic cosmetics undergo formulation and safety considerations just like other cosmetics.
But neither should you assume that any cosmetic can withstand being repeatedly baked in a hot car or left on a sunny windowsill.
Natural doesn't mean indestructible.
Should you put organic cosmetics in the fridge?
Not automatically.
This has become something of a beauty trend, but colder isn't necessarily better.
Products should generally be stored according to the manufacturer's directions. Unless the product specifically recommends refrigeration, repeatedly moving cosmetics between very cold and warm environments isn't necessarily desirable.
A cool, dry place away from direct sunlight and excessive temperature fluctuations is generally a much better solution.
And remember that bathrooms themselves can become warm and humid.
7 things to do with your beauty products during a heatwave
1. Get them out of direct sunlight
Move products away from sunny windowsills and dressing tables receiving prolonged direct sun.
2. Never leave your makeup bag in a hot car
Take it with you — particularly if it contains lipsticks, creams, liquid products or perfume.
3. Find the coolest cupboard in the house
A dark bedroom cupboard or drawer can often provide a more consistent environment than a warm bathroom.
4. Keep lids firmly closed
Reducing unnecessary exposure to air, moisture and contamination helps protect your products.
5. Keep fingers out where possible
Use clean applicators or spatulas with jars. Introducing microorganisms with your fingers can add another challenge for the product's preservation system.
6. Look — and smell — before applying
Has your moisturiser separated?
Has your serum changed colour?
Does your oil smell rancid?
Has your lipstick developed an unusual texture or smell?
Changes don't always mean a product has become dangerous, but significant or unexplained changes are a good reason to stop using it and check with the manufacturer.
7. Check the PAO symbol
Look for the little open-jar symbol on your cosmetics — perhaps 6M, 12M or 24M. This indicates the recommended period of use after opening.
Hot, inappropriate storage isn't a reason to extend it.
One important organic beauty distinction
There's another point worth remembering when shopping for organic cosmetics.
“Natural” and “organic” on the front of a product aren't the same thing as independent organic certification.
COSMOS certification establishes detailed criteria covering ingredients, processing, manufacturing, storage, packaging, labelling and certification.
The Soil Association is one of the certification bodies working with the internationally recognised COSMOS standard in the UK.
So if choosing organic beauty is important to you, don't rely solely on beautiful green packaging or botanical imagery.
Look for recognised certification.
Your summer beauty rule: treat cosmetics a little like food
Perhaps the easiest way to think about your summer beauty collection is this:
If you wouldn't leave something delicate sitting in direct sunshine for hours, don't do it with your skincare either.
Your cosmetics are formulations containing oils, water, waxes, botanical extracts, pigments, fragrances, antioxidants and many other ingredients.
They deserve appropriate storage.
And whether your bathroom cabinet contains conventional cosmetics or certified organic beauty, the same basic summer rules apply:
Keep them cool.
Keep them dry.
Keep them clean.
Keep them out of direct sunlight.
And pay attention when a product suddenly looks, smells or feels different.
Because during a heatwave, protecting your beauty products can be just as important as changing your beauty routine.