Why does cosmetics "vomit" on a plane?

Many passengers said that when they flew to Tibet, Yunnan and other high-altitude areas, as soon as they opened the eyeliner, the eyeliner would flow out of their hands; as soon as they opened the sunscreen, half of the tube would "spit out"...
In fact, these "vomit" skin care products have one thing in common: the bottles or jars are not completely filled, and some air remains in them.
When producing and storing cosmetics at low altitude, the internal air pressure is equal to the external atmospheric pressure. At this time, the internal and external pressures are in equilibrium, and the outer packaging will neither shrink nor expand.
When transporting cosmetics from low altitude areas to plateaus, the internal pressure is higher than the external pressure because the air pressure on the plateau is lower.
This portion of air, brought from low-lying areas, will expand in volume due to the change in external air pressure. Combined with a bumpy journey, the expanded air mass will mix with skin care products.
If the outlet of the outer packaging is relatively narrow, such as the neck of a hose, its cross-sectional area is sharply reduced compared to the body of the tube, and the flow rate increases sharply.
There are two important conditions under which cosmetics can cause altitude sickness. The first is that the internal pressure is greater than the external pressure, and the second is that the outlet is relatively small.
Based on these two conditions, we can take a number of targeted measures to prevent the occurrence of mountain sickness.
The first thing you need to do is let the air out of the room. If you have reached a plateau, shake the bottle or jar before opening the skin care product to allow the product to sink to the bottom and the air to rise to the top. This way, when you open the lid, the air comes out first.
If you haven't already set out, you can use small soft bags to pack your skincare products, then squeeze the air out of them. This way, there won't be a pressure difference between the inside and outside of the container.
If you are traveling to the plateau by train, car or other means of transport, another method is to open the lid of your cosmetics from time to time to maintain the balance of internal and external pressure. If you are traveling by plane, this method may not be suitable.