The sun protection factors given on the packs are based on strict recommendations for use. Cream must be applied at least half an hour before sunbathing, for example, and even water-resistant products should be reapplied several times a day. It is also important to apply the correct quantity: product tests to determine the protection factor are based on 2 mg per cm2. As a general rule, this means that a teaspoon is enough to cover the face. If applied correctly, a 150 ml bottle would therefore only be enough for 5 applications.