Homemade masks are fun and can be beneficial - and there a myriad of recipes out there. Keep in mind that ingredients such as lemon juice, cinnamon, or tea tree, while prominent in many skincare products, can be irritating or dangerous to the skin if used incorrectly. Cooking oils can be comedogenic. Another issue is contamination and growth of bacteria. So if you make a mask, use it and toss any leftovers. Retail and professional skincare products are carefully formulated to address specific skin concerns. So if you make your own, be sure to know what the ingredients are good for and use them in a safe way.