Fact sheet on yeasts

General
Yeasts are unicellular fungi mainly assigned to the taxonomic group of sac fungi (Ascomycota). In cosmetic products they are tolerated only in low numbers. Detection can, for example, indicate insufficient hygiene measures during manufacture, filling or storage. ISO 17516 also specifies limits for the total number of aerobic microorganisms. For cosmetics in general the limit is 1000 CFU/g. For cosmetics for children under 3 years of age and for applications in sensitive areas such as the eyes, mouth, or the intimate area, the limit for yeasts is 100 CFU/g.

For the yeast Candida albicans, ISO 17516 requires absence in 1 g of cosmetic product.

→ Information on another taxonomic group from the kingdom of fungi: see the fact sheet on moulds

Origin / Occurrence

• Yeasts are widespread in our environment (e.g. soil, plants, air, water, humans …)
• They can enter cosmetic products via raw materials, packaging materials, the production environment or personnel.
• There is an increased risk of yeast growth especially in water-containing and poorly preserved products.

Significance

• Yeasts can be indicator organisms for hygiene deficiencies during manufacture or for insufficient preservation. At higher microbial counts they can cause premature spoilage.
• Detection indicates a potential impairment of the microbiological quality of the cosmetic product.
• Yeasts can also grow in the absence of oxygen and produce ethanol. Unlike most bacteria, yeasts have the special ability to grow at low water contents and/or low pH values.
• Candida albicans is of particular significance among yeasts in cosmetics. As this yeast can also cause infections in the intimate area, it is unwanted in cosmetics.

Growth conditions

• Temperature:
  
  • Optimum: +25 °C to +35 °C
  • Minimum: 0 °C
  • Generally no growth above +50 °C
• pH value: Growth at pH 2.0 to 8.5 (for many the optimum is pH 4.0 to 6.0).
• a_w value: According to ISO 29621 cosmetics with an aw value of less than 0.75 are considered low-risk, as microorganisms generally cannot multiply at this water activity.
• Some yeasts have osmophilic/osmotolerant or acid-tolerant properties. This means these species can also grow at low water content and/or low pH (e.g. Zygosaccharomyces rouxii up to an aw value of 0.62).
• Oxygen requirement: aerobic respiration or anaerobic fermentation (facultatively anaerobic).

Inactivation by heating

• At +72 °C with a minimum exposure time of 2 minutes most yeasts are inactivated (Note: check core temperature).
• Yeast spores are reliably inactivated at a core temperature of +80 °C.

1. Check implementation of cleaning and disinfection:
   1. Hygiene plan with information on how cleaning and disinfection are to be carried out, e.g. dosing, contact time, use of suitable and clean materials and cleaning cloths
2. Train employees regarding potential errors and corrective measures
3. Repeat cleaning and disinfection
4. Verify effectiveness through on-site inspections and follow-up testing (e.g. contact plate and swab tests)

1. Check water systems and piping for correct function and condition. Avoid stagnation of water in e.g. pipes, systems, hoses …
2. Regularly check water systems and piping microbiologically and technically (observe maintenance intervals)
3. In case of contamination of water systems act immediately and initiate measures. Involve specialist companies as needed
4. Verify effectiveness through regular follow-up testing

1. Inspect incoming goods for e.g. shelf life, packaging, deviations or microbiological abnormalities
2. This also applies to the material before it is used in production. Do not use raw materials if contamination is suspected
3. Check microbiological specifications. If necessary, request laboratory testing of suspicious products or request results from the supplier
4. Verify effectiveness through follow-up testing

1. Ensure adherence to the formulation
2. If necessary, perform a preservative efficacy test (challenge test)
3. If necessary, adjust the preservation system
4. Verify effectiveness by repeating the preservative efficacy test

1. Check and document production processes
2. Train personnel
3. Verify effectiveness through regular microbiological product testing

1. Review workplace organization in the facility
   1. Separate work areas, equipment and utensils
   2. Separation of "clean" and "unclean" areas and activities
2. Train employees regarding potential errors and corrective measures
3. Verify effectiveness through on-site inspections and follow-up testing