I've seen it written it can have a shelf life of up to 1 year, but you can find unrefined oil that has a shelf life of 30 to 60 days, so be careful when you are buying hemp seed oil - choose one with a long shelf life or ask your supplier if you're in doubt! Most of the time, this oil is considered to have a 3 to 6 month shelf life.
It is considered a dry oil - like camellia or hazelnut oil - so your products will feel less greasy if you include hemp seed oil.
Let's be honest, hemp seed oil isn't your usual carrier oil. For some people and organizations, hemp seed and its derivatives are a political matter, so they want to spin the information to show how useful and awesome it is in every possible situation. So I'm going to share with you information that I've been able to confirm, as opposed to the wild claims that make you wonder if hemp seed oil can bring world peace, end hunger and famine, and make us all look ten years younger!
Hemp seed oil contains phytosterols, mostly in the form of ß-sitosterol at 3.6 to 6.7 milligrams per kilogram of oil. Compared to something like sea buckthorn oil at 522 milligrams per 100 grams of oil, this isn't a lot. Phytosterols can behave like cortisone, reducing itchiness, redness, and inflammation. It also contains about 800 to 1000 mg per kilogram of oil tocopherols, mostly in the form of gamma tocopherol (about 85%). This is a lovely amount of Vitamin E, which will help soften your skin and extend the shelf life of the oil.
Hemp seed oil contains two main polyphenols - cannabinoids (oil soluble polyphenol) and carotenoids. There doesn't seem to be any evidence that cannabinoids have any benefit for your skin, but we know the carotenoids behave as free radical scavengers and lend colour to the oil. The more carotenoids, the darker the colour of the oil. Carotenoids may offer anti-inflammatory benefits to a product.
The oleic acid in hemp seed oil is moisturizing and cell regenerating, and offers softening properties. It is well absorbed by the skin and offers anti-inflammatory benefits. The linoleic acid helps restore barrier properties, acts as an anti-inflammatory, and moisture retainer. Studies are showing people with acne may benefit from an increase of linoleic acid on their skin. But it's the uncommonly found gamma linolenic acid that gets my attention!
Gamma linolenic acid is found in oils like borage and evening primrose oil. It's a great anti-inflammatory, and studies have shown it can increase barrier repair in our skin faster than linoleic acid. It is absorbed quickly, and helps retain moisture and reduce itchiness in skin. There are some studies showing it may help people with acne prone skin. At up to 5% GLA, hemp seed contains a lot less than borage oil (23%) or evening primrose oil (9 to 12%), but you can still get the benefits of GLA by using hemp seed at 20% or more in your products.
The more refined the oil, the lighter the colour and the longer the shelf life. Virgin hempseed oil contains more tocopherols than highly refined oil and contains more polyphenols. So choose your oil wisely - you might be happy with a reduction in Vitamin E for a longer shelf life!
Store hemp seed oil carefully - a cool, dark place is fine, but the fridge is better! If you want to formulate with hemp seed oil, ensure you have a very clear "best before date" on the label. (Can you tell I have some experience with this oil?) Add 1% Vitamin E to anything you make to help with anti-oxidation, and think of including some chelating ingredients to extend the shelf life.
Hemp seed oil is lovely in a facial serum or moisturizer, a high linoleic acid body lotion for the winter months (and summer months, and every other month in between), or an apres bath or shower oil for all that GLA goodness. As it is considered a dry oil, combining it with something like grapeseed, hazelnut, or avocado oil might be a little too dry feeling, but if you want that powdery feeling in your products, hemp seed oil might be a good addition! Just ensure you don't put it in something you'll want to have around for a while...