Microscopically, a plant is made up of units or cell, many of which are no longer living and serve only the skeletal function of mechanical support, e.g. the wood of tree trunks. Others are living and serve a variety of functions in the life process of the plant. The individual cells are bounded by a cell wall, (consisting largely of cellulose), and within this wall is a space in the case of dead cells and liquid in the case of living cells. It is the cell content that is of interest to cosmetologists for providing the basis of botanical extracts.

The cell content consists largely of water in which is dissolved or suspended various organic and inorganic materials. This is not just a haphazard mixture or emulsion but a highly organised system since the cell is, after all, a living unit carrying out the processes of life. It is not surprising therefore, to find extremely complex substances present; for instance proteins, amino acids, oils and fats, mineral and organic salts, to name but a few.