Just for your interest, they do sell L-ascorbic acid at The Ordinary.
I put it in distilled water, put a very high concentration, way more than 5% very likely, and apply the same day both on face and hair. Very cheap.
I also use the granactive retinoid 5% and find it very good for my skin! Not sure where to find the tretinoin, can you recommend one or where to get it? Need a dermatologist?
Any else product from The Ordinary that you recommend for wrinkles/signs of aging?
They do have a LAA powder and some 8% mix with 2% arbutin. All other LAA's are in a suspension and LAA is only water soluble. Any other carrier is ineffective. The powder is good, if you know how to make your own vitamin C serum (with adding glycerin, tocoferol, ferulic acid, etc).
Vitamin C works best when its concentration is around 15-20%. Any lower will merely have photo-protective effects, any higher wil just result in irritation and possibly formation of free radicals which has the opposite effect.
Vitamin C only works on skin, sprinkling it on your hair will at best dry it out a bit and have a bleaching effect.
Tretinoin is not a brand or anything, it simply is the name of the vitamin A acid. Personally I don't have any experience with using tretinoin as I'm still in my early 20s and never had acne. I know several people who have used it for either acne or wrinkles, and most seem to be happy with the results.
My mother in law uses Retin-A (and yes, this is a brand name) and it seems to not be too drying and greasy. But this can only be prescribed by a dermatologist, you won't find it being sold freely (unless you buy it an online pharmacy).
Well, once wrinkles or other signs of aged skin are set its hard to revert it. Preventing is the best, and nothing works better than daily use of at least SPF30 sunscreen. Stress and diet (and probably many others) have their contribution as well, but is minor compared to the damage of uv.
The things that work best (not only for wrinkles, sunspots, acne or rosacea) are always on prescription, such (20%) azelaic acid for rosacea and pigmentation, hydroquinon for pigmentation and tretinoin for acne and aged skin.
There are a few things that can really make your skin look better with consistent use, such a vitamin C, niacinamide, hyaluronic acid, low % azelaic acid. But their results are by no means very thrilling. If I would have to pick my favorite TO product, it would be the 10% niacinamide + 1% zinc serum. Very cheap, 30ml bottle lasts forever and really gives results.
It fades pigmentation somewhat, controls sebum production and is very hydrating. With wrinkles you want to keep your skin as moisturized as possible.
As I said, it's trial and error and the possibilities are almost endless. You just gotta find that sweet spot what works for you. And if nothing works, there are still (very pricy) laser treatments such as (CO2) fraxel lasers, etc or real surgical options.