"The reason for using primer is to ensure that your foundation is lighter," said Caroline, so you avoid the heavy, cakey look and feel. "Primers with a green, colour correcting undertone are especially important if you have rosacea , sunburn or any kind of redness. The trick is to create a puzzle effect with it. I will strip back skincare on the T-zone and just apply a mattifying primer. When I then go to put foundation and powder on, I need very little. The more powder you put on the skin, the less refined makeup looks." And while many of us shy away from silicone in primer, Caroline champions it. "I think it makes the skin look really smooth."