Antimicrobial preservatives are added to non-sterile dosage forms to protect them from microbial growth or from microorganisms that are introduced inadvertently during or after the manufacturing process. Antimicrobial preservatives should be added if sterile articles are packaged in multiple-dose containers, thus they inhibit the growth of microorganisms introduced from repeated withdrawal of individual doses.

Preservatives are natural or synthetic chemicals added to prevent decomposition by microbial growth or by undesirable chemical changes in various products like foods, pharmaceuticals, paints, biological samples, wood, etc. Thus, preservatives are added to various foods and pharmaceuticals in order to enhance their shelf-life.

Chemical preservatives do not totally keep products free from getting spoiled by microbes, rather they slow down the spoiling process. Preservatives are not commonly added in frozen and canned foods. In processed foods, the harmful bacterium which may contaminate the food is killed by different processes, which are assumed to be beneficial for preserving the products, but they can also add harmful substances.

During the processing of natural food, it is crushed, heated, and added with chemicals that may destroy all the nutritional value of the food. Often, additives are added to the products to put back some vitamins and nutrients that were lost when the food products were processed.

Preservatives are added to keep the food fresh and free from spoiling. Some commonly used natural preservatives are vinegar, salt, and sugar. Most of the synthetic food and cosmetic preservatives are considered safe but some of them were found to be carcinogenic and toxic, and therefore have limited uses. Generally, all synthetic chemical additives and preservatives may be avoided because most of them are not tested properly.

The food colouring chemicals have harmful effects, therefore use of food colourings made from synthetic chemicals should be avoided. The efficiency of antimicrobial preservatives depends on their ability to kill live cells; thus their toxicity is unavoidable. Many plants and compounds of natural origin (like essential oils) have the power to destroy bacteria, yeast, and fungi; however in many cases these substances produce toxic effects to humans.

For example, citrus or grapefruit seed extracts have natural antimicrobial properties and some of their constituents are responsible for life-threatening hormonal imbalances.

An antimicrobial agent should possess the following ideal characteristics:

1. It should be efficient against many species of microorganisms.
2. It should possess high water solubility or easy dissolution in commonly used cosmetic ingredients.
3. It should be safe and should cause no irritation.
4. It should be neutral with no effect on product pH.
5. It should not have any effect on product efficiency.
6. It should not have any adverse effect on product appearance.
7. It should be stable over wide range of temperature and pH.
8. It should be available readily and its supply should be stable.
9. It should be economical.

Table enlists some antimicrobial agents used in pharmaceutical products: