Panthenol is an alcohol that is processed by our body to become pantothenic acid - a water soluble vitamin, Vitamin B - a major constituent of our hair. This is why you see it in most hair care products, and why an entire hair care line is named after it!
Panthenol for hair care products is a fantastic addition at 2% to 5%. It builds a thin moisture film on the surface of your hair (film former) and makes it shine without oil or greasiness. In addition, it can penetrate the cuticle of your hair and brings moisture to the cortex! This means you get good manageability and pliability of your hair, and it is better able to cope with brushing, wind, and other non-hair friendly things. Finally, it could give your hair more body! Studies have shown that 2% left on for 2 minutes can actually swell the hair shaft, making it seem thicker! (So use it up to 5% in your conditioner or leave in conditioner!)
For your body care products, panthenol is a must have, again at 2% to 5%. It penetrates deep into the epidermis to bring water into the stratum corneum, and can retain water in the skin. (It's a humectant - that's what it does!) Unlike some humectants, it will not leave a sticky feeling to your products. Studies have shown that not only is it moisturizing, but it can actually heal inflammation, sunburns, and wounds at 5% in a lotion by up to 30% quicker than a lotion without panthenol. And it's good for people with sensitive skin and babies!
It is very soluble in water, soluble in alcohol and glycerin, and not at all in oils. It's not sticky, so you can use it as a humectant, although I'd use it in conjunction with another humectant because panthenol gets a little expensive! So you're going to add this to your cool down phase at 2 to 5% for maximum awesomeness.
Panthenol comes in the D and L format - d for the right handed molecule, l for the left handed molecule - but our bodies only process the D form. You can get it in powdered or liquid form. I prefer the liquid form because it's easy to add in the cooling down stage, but the powdered stuff works just as well (add to the water stage). (The powdered form is a salt form of panthenol designed for easy solubility.)
Let's get formulating with panthenol (although if you've read any of my hair care posts, you know I include it in everything!)