Soy bean is another oil with a ton of linoleic acid (C18:2, 53%), some oleic acid (C18:1, 29%), palmitic acid (9.8%), and linolenic acid (C18:3, 8%). The three fatty acids with double bonds are going to cause some problems with your shelf life, but soy bean oil contains about 700 mg/kg of tocopherols, so there are some natural anti-oxidants built in - and the Vitamin E is going to help with skin softening and moisturization.
What takes soy bean oil from good to awesome? It contains about 6.3% omega-3 fatty acids and 51% omega-6 fatty acids, both of which have great benefits for your skin. And it contains high levels of phytosterols (327 mg per 100 grams of oil - the highest of our carrier oils!) and isoflavones!
The phytosterols in soy bean oil help soothe wind chapped, sun burned, itchy or inflamed skin, so this is an ideal inclusion in a lotion or bath oil. Soy phytosterols can soften hair and lessen the electrostatic charge that can lead to "fly away" hair (does anyone have that problem any more? I never see it advertised as a feature in hair care products!)
The isoflavones in soy bean oil - genistein and daidzein - can behave as phytoestrogens when ingested; there is no evidence to show they behave this way on your skin. In soy bean oil, they behave as anti-oxidants that protect against peroxidative damage, which can cause rancidity.
Soy bean oil is a light weight oil with medium comedogenicity. It's easily absorbable, and can be anti-inflammatory. It has a shelf life of about 6 months to a year, so you'll want to add a little more Vitamin E and some chelating ingredients to your lotion to extend that life span!
Personally, I love soy bean oil in pretty much everything. I use it in hand and body lotions, and I use it as the oil binder in my bath bombs (link to my bath bomb recipe here and here, and link to bath cupcake recipe here). Because it is a light weight oil, try substituting it for another light weight oil you love - sunflower, safflower, sweet almond, or apricot kernel oil - in your favourite recipe. It is a great, longer shelf life oil you can substitute instead of hemp seed oil! With a similar fatty acid profile (hemp seed has less oleic acid) and similar benefits for skin, you can create a lovely lotion with a much longer shelf life for far less money.
Join me tomorrow for formulating with soy bean oil!