Causes of Sour Smell in the Formula

The sour smell that developed in the formula after 2-3 weeks could be due to several factors:

• Microbial Contamination: Although the formula contains the preservative Phenoxyethanol SA, if the manufacturing process is not sufficiently clean or the containers used are contaminated, microorganisms can grow. Some microorganisms can break down components in the formula and produce substances with a sour odor.
• Preservative Efficacy: The preservative Phenoxyethanol SA works effectively in the pH range of 2.0-6.0. If the pH of the final formula is outside this range, its effectiveness in inhibiting microorganisms might be reduced. Additionally, uneven dispersion of the preservative within the formula could also be a cause.
• Ingredient Instability or Degradation: Some ingredients in the formula, such as SPF Protect Ultra II, Milk Lotion Maker, or Satin Cream Maker, may degrade over time, especially under unsuitable conditions like high temperature, sunlight, or temperature fluctuations. This degradation can lead to the formation of new substances with unpleasant odors.
• Ingredient Incompatibility: Although individual ingredients may be safe, combining them in inappropriate proportions or methods can lead to reactions between them, resulting in separation, changes in texture, or the creation of sour-smelling substances. The provided formula uses two emulsifiers (Milk Lotion Maker and Satin Cream Maker), and the mixing method and conditions must be carefully considered for long-term stability.
• Water Quality: If water that is not purified or properly sterilized is used, it can be a source of microbial contamination introduced into the formula from the beginning.

Having the MySkinRecipes team test the formula in the lab is the correct approach to determine the exact cause of the issue. Considering the storage environment is also important, as external factors influence the stability and microbial growth in the formula.