1, the amount of preservative added is not enough. Generally, the dosage of preservatives can be less for products with higher concentration, and higher for products with lower concentration.
2. The preservative was added too late. Preservatives can only work if the product is not corrupt. Once the product is corroded by bacteria, it will not work if it is added. Most preservatives need to be cooled before being added.
3. The production environment is polluted by bacteria. In the production process of liquid detergent, because it has been dealing with water, the environment is usually humid and easy to breed bacteria.