Abbie mentions that you can't really stop a foundation from oxidizing, you just need to know which ones do and to avoid them. "Make sure that when you are purchasing a new foundation, you take a sample. Wear it for a day and then go back and purchase it if you are happy with the overall colour and effect," she said. "So many people don't do this and then end up with foundations they can't use." And if you're abroad somewhere warm, you're likely to catch a tan, so Abbie suggests shopping for foundation with a yellow undertone. "Try not to go for pink or neutral tones, as they are less likely to match the rest of your body. Look for warmer tones."