Shampoos are basically a liquid soap (detergent), to which a variety of moisturizer ingredients have been added, to have a certain conditioning effect on the hair.
300 ml water
15 ml decyl-glucoside
6 tsp (12 g) salt
1 tsp coconut oil
1 tsp honey
1 tsp glycerin (from vegetable source)
1 tsp almond oil
1 tsp lecithin
1 tsp guar gum
15 drops essential oils
Recipe: mix the ingredients listed above, one by one, in low heat. Lecithin requires more time and heat to dissolve into the oils. Add guar gum little by little, while stirring vigorously. Confirm that the pH is around 5.5, otherwise use lactic or citric acid to adjust it. Let the shampoo cool and add the essential oils. The shampoo will thicken in the following days.
All of these ingredients are from natural sources. Glycerin can be extracted from vegetable oils (however nowadays is also produced by chemical synthesis); Lecithin is a natural emulsifier (helps oil mixing with water) and is extracted from soy beans or eggs (it's also eaten as a food supplement); Guar gum is a powder obtained from the crushed seeds of an Indian tree (Cyamopsis tetragonolobus), it's used as a thickener (creates the gel texture of the shampoo), and it's added as an ingredient of ice-creams and drinks. Different ingredients are used as emollients (moisturizers), giving the feeling of a soft hair and skin after use: glycerin, honey, almond oil and coconut oil. The essential oils impart some therapeutic effects and a nice smell.
Decyl glucoside is a chemical. It's obtained from reacting glucose from fermented corn starch, with an alcohol extracted from the coconut oil. While still a chemical, it's the mildest and most natural surfactant, to produce some foam. Nevertheless, this shampoo will still foam little, but leaving your hair feeling clean, light and soft. With the exception of decyl glucoside, all the other ingredients are completely natural. Decyl glucoside is derived from natural sources, is very mild for the skin, and is readily biodegradable in the environment. Almost all shampoos have more harsh surfactants, that are more irritant, and some even toxic for the body (see below). Some very strict organic shampoos use decyl glucoside as the best alternative. In this shampoo, we only used 5% of total volume, so it will lather just a little.
Although the hair will feel clean, fresh and soft, the shampoo will not spread easily. I am currently working on a solution for this.
If you want to be close to 100% natural, you can do a natural shampoo, based on castille soap (made from olive oil and lye - sodium hydroxide, provided that you have used the exact amounts of each to ensure all lye reacted with the oil to form the soap, see soap calculator). However, you cannot drop the pH to 5.5, because that destroys the soap. The alkaline pH (~8.5) of a soap-based shampoo is more harsh for the hair, and leaves it less soft. It can also damage it more easily. Ideally, the pH of every skin and hair product should be around 5.5, because that's their natural acidity. You can adjust the pH by adding vinegar (but this creates smell), or by adding lactic acid or citric acid (which are chemicals derived from bacteria fermentation of milk and lemons). Lemon juice is not good because it gradually bleaches the hair. A soap-based shampoo will be more thick and lather well, but leave the hair less soft and light.
An even more natural alternative is to use extracts from plants that contain saponins, such as soapwort, Soapnuts (Sapindus mukorossi), Shikakai (Acacia concinna) or Quillaja (Quillaja saponaria). These plants create can foam, when boiled, but the effect is much less than that of synthetic surfactants or soap. These plants do not lather as much as synthetic surfactants. I haven't experimented with Quillaja or Shikakai extracts but I have heard that both create quite good shampoos. I will try it and write about it in soon.
Ingredients to avoid in shampoos and cosmetics: parabens, phthalates and synthetic fragances, laureth sulfates, lauryl sulfates, propylene glycol, quaternium, butyl cellosolve, isobutene, dioxin, sodium myreth sulfate, DMDM hydantoin, carmine, talc, triclosan, DEA, MEA and TEA, cocoamide DEA, chroloacetamide, lauramide DEA, ZPTO, PEG-55. Vitamin E, honey or salt, can be used as natural preservatives.
You would be shocked to know how much toxic chemicals do normal shampoos contain. In fact, even organic and all natural labeled shampoos still have chemicals, sometimes even harsh ones! (article the truth about ingredients) However, there are a lot of organic brands which have been using ingredients similar to the one listed above.