792 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and, since it is soluble in rubber, may produce eruptions even when rubber gloves are worn. Concentrations of ethylene oxide used in practice have been given as 500 mg 1-1 of air, or preferably nitrogen, for 4 h at room temper- ature and also 10-15% in air or nitrogen overnight. Special equipment is not essential, although chambers suitable for preliminary evacuation are sometimes employed. 2.5 Filtration Numerous methods of filtration are available for sterilizing various types of liquids and for air sterilization. For large-scale treatment of water and aqueous solutions, it is usual to employ either diatomite filter candles in a specially-designed unit or special grades of filtering mats in a con- ventional filter-press. Filters intended to remove all micro-organisms from a liquid or vapour might appear to need a maximum pore-size below about 0.2 gm. In practice, adsorptive filtering materials do not rely solely on mechanical trapping of micro-organisms and will usually operate satis- factorily with a maximum pore-size of 1-2 gm. It is important to ensure that the correct sterilizing grade of filtering agent is used (not the coarser clarifying grades) and to see that the filter is properly installed without accidental damage or channelling, e.g. around the edges of the mats. Excess pressure intended to improve flow rates during use will often damage a sterilizing filter unit and allow micro-organisms to pass careless cleaning efforts may have a similar effect. Filters for sterilizing applications must be sterilized and operated within sterile equipment in particular, pipe-lines and vessels taking the filtered material must obviously be presterilized with the aid of saturated steam or chemical sterilants, or the product will rapidly become contaminated again. Sterilization by filtration is one of the most suitable and economical ways of handling large volumes of mobile liquids, such as shampoos, but it calls for considerable skill and experience to ensure routinely good results. Frequent microbiological tests are necessary to give assurance that steril- ization is being achieved and that filters have not been damaged. 2.6 Chemical sterilization References are made in this monograph to sterilization by means of chlorine (e.g. solutions of hypochlorite yielding 200-250 ppm of available chlorine) and formalin (e.g. 0.5% equivalent to 0.2% of formaldehyde). Used in accordance with the operating conditions prescribed, especially with respect to preliminary cleansing, these chemical sterilants will prove suit-

HYGIENIC MANUFACTURE AND PRESERVATION 793 able for the maintenance of plant hygiene. In general, chemical sterilants cannot be incorporated as ingredients of products as they necessarily have a high degree of intrinsic chemical and biological reactivity they are liable to alter the product characteristics to a marked extent or to elicit adverse cutaneous reactions. However, just as a chemical disinfectant will effectively sterilize clean surfaces of equipment, so a small percentage of a bactericide or fungicide may exert a sterilizing action in a cosmetic product which has been prepared in a clean and hygienic manner. The possibility of using preservatives to achieve self-sterilizing properties in cosmetics is dealt with in Appendix B the principle, in brief, is that the preservative should not be employed to achieve sterility at the time of manufacture (which should depend on other measures) but should be aimed at the destruction of limited numbers of contaminants entering the product at a later stage. 2.7 Flaming For microbiological test procedures, including the taking of samples in the production area, a rapid method of sterilizing hard surfaces of small pieces of equipment is often needed, e.g. temporarily-opened necks of bottles and also wire loops used for inoculating culture media. Direct heat- ing in an open flame is employed and should be carried out thoroughly, in close proximity to the point where the flamed equipment will be used quick passage through the flame gives reassurance but not sterility. Metal instru- ments (scissors, etc.) may be sterilized by swabbing with alcohol, which is then burned off this is a less effective procedure than direct flaming but is not so detrimental to the cutting edges of instruments. 2.8 After-care of sterilized materials Equipment and chemical products that have been sterilized will, in general, only remain sterile if the access of fresh contamination is rigorously avoided. This aspect is discussed in detail under plant sterilization as it affects production equipment and the same considerations apply to raw matehals, intermediate and finished products. Even in circumstances where the aim is to achieve a low microbial count rather than absolute sterility, it is clearly desirable to restrict adventitious contamination as much as possible. Emphasis has therefore been given to matters, such as taking care to see that lids fit closely and that they are securely in place whenever possible. The fact that contamination is a dynamic process should be borne in mind. With faulty storage, product bearing a low level of contamination