We have been told many times that cosmetics are a rip-off and that a $150 pot of beautifully packaged, expensively marketed anti-wrinkle cream may be no better than a $15 jar from the supermarket. So there might be a lot to be gained from making your own, not only financially, but also from the fact that at least you know what you've put in it.
In many respects, that's true. But as with almost everything, it's never quite as simple as you think. Before embarking on a magnificently earth-motherish expedition into the manufacture of natural hand creams using your own lavender oil, beeswax from your own hives, and purified rainwater, it's always helpful to stop and consider the practicalities. It is indeed perfectly possible to make useful, natural, and highly attractive skin creams, hair washes, and perfumes. There are just a few considerations to bear in mind about costs, safety, and the amount of time you have available.
The first thing to realise is that natural ingredients, sourced from living things, will rot. Cosmetic preparations will grow bacteria, and they will also go rancid. Neither of those is good for you, so you have two choices: make them fresh and use them quickly, keep them in a cool place, if not actually in the fridge; or use preservatives. Be particularly aware that oils go rancid: this applies to essential oils, which may smell not at all as you expect them to after twelve months' storage and carrier oils such as almond and olive. You will need to buy small quantities and use them promptly.
The preservative question is interesting. Many cosmetics now loudly proclaim the absence of parabens, which have been recognised as potential carcinogens. Of course, you aren't guaranteed to develop cancer by using preparations with parabens in them, but if you can use something else instead, it's probably a sensible move.
There are still some risks, however, even with the less obviously worrisome preservatives. Two commonly used substances are DHA (dehydroacetic acid, which despite its name, is not dried vinegar!) and benzyl alcohol, sometimes used in combination with DHA. If you would like to look at some scientifically-based comments about possible risks with these two preservatives, try here for DHA and here for benzyl alcohol.
In the end, you just have to weigh up the relative risks of bacterial contamination against potential hazards from the preservative. And if you want to be certain you are minimising the risks, go for the "make it fresh, use it fast" approach, which is strongly advocated in a fascinating New Zealand book. Elizabeth Francke wrote "The Make Your Own Cosmetic and Fragrance Book for New Zealanders" in 1980. It is full of historical snippets and recipes. It also gently and humorously reminds us of the assorted madnesses surrounding female appearance. An updated version published in 2005 called "Make Your Own Cosmetics and Fragrances" is available from Raupo Publishing (part of Penguin NZ), ISBN 0790010038. The recipes are "from scratch" preparations and some require a certain amount of time and patience, but if you want plain, pure, and natural, this is probably a good place to start.
If you would like to try cosmetic manufacture using easily obtainable ingredients from an online seller, have a look at the GoNative website. This is a New Zealand business, which supplies individual ingredients such as essential oils, carrier oils, vegetable butter, waxes, and preservatives. They also provide ready-made bases for items such as body butter, moisturisers, lip balms, and liquid soaps, and have a range of recipes and instructions. While making your own is cheaper than many commercial products, the costs are not negligible. At the time of writing, essential oils from this supplier are around $10 to $20 per 60ml, with some, such as pure rose oil, being up to $80 for 5ml. Carrier oils are mostly in the $6-$15 per 100ml range, waxes such as beeswax are around $6 to $12 per 100g, and preservatives, used in very low amounts, are $15-$20 per 100ml.
As a final caution, there is always the issue of individual variation to consider. Most people find lanolin (from sheep's wool) a wonderful soothing substance for the skin. Some of us react to it and go out of our way to avoid it. Some essential oils will generate allergic responses for some users and lead to itching and scratching instead of relaxing luxury. As Elizabeth Francke sensibly suggests in her book, try a patch test of any new ingredients on your skin and check over a couple of days for any kind of reddening, itching, or other reaction.
All those things considered, it is still a very pleasurable activity to make your own cosmetics and lotions, and you will get a great sense of satisfaction out of creating something that uses your own fragrance combination and in some cases is even largely grown on your own land.