Generally the answer to this question is going to differ from product to product. When purchasing a product, it is always a good idea to enquire of your therapist or doctor with regards to product application. As a general rule, as long as you are applying enough product to easily cover your face, neck and chest, without leaving a lot of excess that you have to wipe off, you should be alright. In some cases the amount of product that you apply really is important as the result is dependent on volume applied. For example, when applying your sunblock, you should use at least 5ml over your face and neck and chest to get the actual SPF value applicable on to your skin, otherwise you are not adequately protected for as long as what you may think you are.