Where can I buy genuine skin care products and cosmetics?

If it must be guaranteed to be genuine, it can only be official website of those skin care and makeup brands. However, it is more expensive to buy these brands in official website, so it is better to go directly to a physical store or find a more reliable agent to buy them. You can also find a time to go abroad or show yourself, so you can also buy it in duty-free shops in Japan or abroad.