What is a "Natural" Substance?

A natural substance is any plant or animal extract, or any rock or mineral obtained from the earth. They are often contiminated with a host of other substances, which must be removed in order to achieve the required degree of purity before they can be used  as ingredients in personal care products.
Artificial or synthetic ingredients are made when substances are modified by chemical reactions in industrial processses. It is possible for chemists to make exact copies of natural substances . The synthetic versions are identical in every respect to the original, natural substances: the only difference being the cost and the convenience of production.

One example is methyl salicylate (oil of wintergreen) an important ingredient in many essential oils extracted from a variety of plants, including plants of the wintergreen family, from which it gets its everyday name. It has soothing and pain killing properties,and is used in ointments and liniments for rheumatic pains, strained muscles , and minor injuries , and is used as a fragrance and denaturant in cosmetics and toiletries. Manufacturers find it cheaper and more convenient to synthesize methyl salicylate from raw materials obtained from coal tar and petroleum, than to extract it from plants.

Recipes for Herbal Shampoo and Hair Rinse
The following recipes were posted on the internet. Most of the ingredients are entirely natural and so give the impression that the shampoo and rinse must be completely without harmful effects, and the herbs must be good for your hair.

• Herbal Shampoo
  6fl.oz (160ml) distilled water
  half oz (15gm) Soapwort root (Bouncing Bet)
  1 tsp (5ml) castor oil
  quarter teaspoon (2gm) sea salt
  15 drops (1ml) Geranium oil
  15 drops (1ml) lavender oil
• 
  Herbal Hair Rinse
  8oz (220ml) cider vinegar
  1oz (28ml) vodka
  1oz (28gm) dried herbs or 4oz (110g) fresh herbs
  1tsp (5ml) castor oil

A choice of herbs was suggested for dark or light hair, or for treating hair with dandruff.