You can read all across Google different recipes for “Do It Yourself At Home Facial” which typically consist of some mashed up fruits and veggies as well as other natural products from your kitchen. Unfortunately this is not providing you the same level of treatment as professional skincare and [worse] there can be negative drawbacks beyond their ineffectiveness.
First and foremost, mashing up a bunch of grapes isn’t going to have the same effectiveness as grape seed extract or oil. Chemistry and science allow us to extract the actives from whatever ingredient we are using and then test their effectiveness. Suppliers of raw materials test as per required industry standards and provide supporting documentation to prove their effectiveness. Quality, highly effective ingredients are the foundation of any professional beauty brand.
Let’s use raspberries as an example. You could have an entire container and it's possible only a few of those raspberries would even be viable to use to extract active ingredients (which typically comes from raspberry seed). Extrapolating this concept for professional beauty brands- it could take SO MANY containers of raspberries to fulfill the effective amount required within each product especially when you are fulfilling hundreds of thousands of a particular sku. If this is the case, mashing up this bowl of raspberries and applying it on your face to brighten your skin likely won’t have the same effect.
This brings me to my second point- consistency matters! Putting these raspberries in the blender and hoping you just made a brightening mask similar to something off the shelf is not only incorrect but could be dangerous. Laboratory quality mixers and homogenizers, the things used to make your creams silky smooth, cost thousands of dollars and don’t even compare to a blender. In addition, hot plates and scales which keep everything consistent can cost you another few thousand dollars. The danger comes into play with non-organic fruits and vegetables in the supermarket which are covered in pesticides (be wary of organic as well, winds can carry pesticides from other fields onto organic crops). Not to mention the random allergens your food could be exposed to. These can be left on your produce and then when applied to your face topically could have its own set of risks. There is also risk with certain ingredients like using raw egg whites as a natural peel; there aren't any instructions on how long to leave it on, how much to use, etc. and depending on your skin type you could potentially give yourself a minor burn.
Now that you know the risks in DIY beauty care, you can begin to realize why cosmetic companies go through so much testing. It is not only that we want to get it right, it is our responsibility to to get it right as a premium brand who promises effective products to our customer base.