"Oils don't moisturise." -- so how come oils and butters are so great for dry skin and hair? Oils are occlusives, and occlusives slow down the evaporation of water from the skin or hair. Basically, they seal in the moisture.
Oils are not the only kind of occlusive out there. In fact, most occlusives are man made: silicones, mineral oil, cetyl alcohol. Occlusives are very important components of most cosmetics, so if you want to know your product you need to know your occlusives.
The "richer" the product is, the more occlusives it contains. Ointments have the most, followed by creams. Lotions, milks and gels contain much less occlusives. Hair masques contain a lot of occlusives, conditioners less, while styling products usually contain lighter ones in smaller doses.
How do occlusives work ?They create a film over the skin and hair. This seals in the moisture, but may also seal out the moisture. Occlusives might block pores -- silicones, cetearyl alcohol, lanolin and certain oils often do this. Do remember that clogged pores can be very individual -- what might not clog your pores might clog mine, and vice versa.
It is handy to recognise the most common occlusives. That way when you take a product into your hand, you can estimate how "heavy" or moisturising it will be. Also, even the best moisturising ingredients won't give great effects if not mixed with an occlusive (think of licking chapped lips -- they simply dry out even more).
Here is a list of occlusives, from dermatology.about.com :
Which occlusives are the best?Mineral oil feels non-greasy and so it´s used very often, but it isn´t very good in sealing the moisture in. Silicones feel silky and non-greasy, but they might block pores or cause build up. I advise avoiding them in skin care products, they may be used in hair care with caution. Lanolin is thick and tends to block pores, but it´s amazing for lips, heels and elbows.
Plant-based occlusives (oils and butters) are the best kind of occlusives since they are biodegradable, and don't pose health risks. Remember however that every different oil has different properties -- some are more likely to block pores than others, and some are less greasy than others. Obviously different oils are good for different products -- if you are looking for a rich, moisturising product for dry skin, sesame oil or shea butter is a good ingredient -- but these same ingredients won't work for you if you need a light product.
Your hair type determine the kind of occlusives you need in your products. Porous hair loves oil, and dry hair definitely needs oil. Finer hair needs very low amounts of light oil (like jojoba). If you feel your hair is weighed down, chances are there is too much occlusives in your products. You can always add extra oils into your products if your hair needs to be weighed down a bit.
It usually takes a bit of trial-and-error to find which occlusives your hair and skin loves. I have written quite a bit on this blog about many occlusives, so have fun browsing through the archives.