The truth is the oxidisation of makeup foundations is less common these days with new makeup formulations. When your foundation darkens through the day, it is due to various factors:
1) You were using too much moisturiser
Moisturise your skin only where it’s needed, and not on your whole face. There is enough moisturising properties in a sunscreen in your skincare regime. The excess use of serums and moisturisers like the 10 steps of #Kbeauty would not work in humid weather.
Having too much skincare products tends to destabilise makeup formulas by oiling up, or turning the makeup wet over the course of the day. If you have oily skin, you would likely need a toner, a treatment serum, a emulsion on drier areas of your face, and sunscreen.
2) There’s excess buildup of cosmetics on your skin
Let’s be honest here: With oil and sweat acting as a lubricant for movement on the skin, do we really need more primers, colour correctors, sunscreens, liquid foundations and powder on the face? It is like piling a multi-layer cake on a moving layer and expect it to last the whole day. This also happens because the ingredients like oils and fats in makeup can become rancid after reacting with oxygen.
For skin that requires skin smoothing properties, try Shiseido Maquillage Dramatic Skin Sensor Base UV SPF25 PA+++, and RMK LongLasting UV SPF45 PA++++. These are excellent for the humid weather. If you have an oilier T-zone, has bigger pores will benefit from Shiseido Maquillage Peach Change Base CC SPF25/PA+++. And those who react to chemical sunscreen can use physical sunscreen primer base like Hourglass Veil Mineral Primer SPF 15.
The above products will help to smooth out your skin texture (depending on your skin needs), and the Shiseido Maquillage product will neutralise, and add a peachy glow on tired complexions. Then follow up by using either a liquid foundation, cushion foundation or powder foundation. The more products you pile on, the more likely it changes colour due to products turning clammy from your sweat and sebum.
3) The colour pigments in your foundation formula is not resistant to sebum and heat
The newer formulations of foundations in makeup brands today have their foundation pigments coated for colour-staying trueness that keep the colours stablised. Some older foundations and cheaper foundations do not have that, and that means exposure to heat and sebum can change its colour, and appear darker.
4) Body chemistry
There are some people with body chemistry that tend to change foundation colour that is rare occurrence that only happens to a few. If you are wondering if you have this factor, you would notice your foundation changing its colour immediately or in less than an hour.