Uses of sodium dihydrogen phosphate in toothpaste and cosmetics

Sodium dihydrogen phosphate is an inorganic compound, easily soluble in water, it has buffering effect, and other effects such as antibacterial, moisturizing, and chelating heavy metal ions, so it is often used in toothpaste and cosmetics.

I. Mechanism of buffering action of sodium dihydrogen phosphate

When the pH of a solution changes, sodium dihydrogen phosphate can adjust the pH by the following two reactions:
When the solution is alkaline, dihydrogen phosphate ions react with hydroxide ions (OH-) to form phosphate monoester ions (HPO₄^2-) and water, thus reducing the alkalinity of the solution:
H₂PO₄^– + OH^–→ HPO₄^2- + H2O

When a solution is acidic, dihydrogen phosphate ions react with hydrogen ions to form phosphoric acid (H3PO4H3) and hydroxide ions, thus reducing the acidity of the solution:
H₂PO^– + H⁺ → H₃PO₄
Through these two reactions, sodium dihydrogen phosphate is able to buffer the pH change of the solution to a certain extent, keeping it within a certain range.
In addition, it has antibacterial and anti-inflammatory, antimicrobial, and astringent properties, so it will be used in the production of toothpaste and cosmetics.

II. ‌Sodium dihydrogen phosphate uses in toothpaste

• Buffer: Sodium dihydrogen phosphate is used in aluminum hydroxide type toothpastes. In this type of toothpaste, disodium hydrogen phosphate is also used at the same time, which is used in combination with disodium phosphate as a buffer to help stabilize the acid-base balance of the toothpaste to make it more suitable for the oral environment, as well as to avoid water and gas phenomenon due to the dissociation of friction agents.
• Relieve tooth sensitivity: Sodium dihydrogen phosphate can relieve sensitivity caused by oral pH imbalance or tooth wear.
• Removes plaque and calculus: Through its pH-regulating action, Sodium Dihydrogen Phosphate helps to remove these harmful substances, thus protecting teeth and oral health.

III. Sodium dihydrogen phosphate use in cosmetics

a. Buffering agent

Sodium dihydrogen phosphate adjusts the pH of cosmetics to bring it closer to the skin’s normal pH range (around 5.5). Maintaining the skin’s normal pH helps to protect the skin’s natural barrier and reduce skin problems such as dryness and sensitivity.

b. Moisturizer

Sodium dihydrogen phosphate is hygroscopic, absorbing moisture from the air and locking it into the cosmetic product, thus providing a moisturizing effect. This is especially important for skin care products that need to keep the skin moisturized to help improve dry skin conditions.

c. Skin conditioner

Sodium Dihydrogen Phosphate contains carbonate ions, which promotes the formation of the stratum corneum and strengthens the skin barrier function. It also helps to improve skin texture for healthier, smoother skin.

d. Metal Ion Chelator

Cosmetics may contain some harmful metal ions which may have adverse effects on the skin. Sodium dihydrogen phosphate can bind with these metal ions and prevent them from causing damage to the skin.

e. Preservatives

Due to its high solubility, sodium dihydrogen phosphate can make it difficult for microorganisms to grow and multiply, so it can be used as a preservative to extend the shelf life of cosmetics.

IV. Conclusion

Sodium dihydrogen phosphate is often used in toothpastes and cosmetics due to its buffering effect. In addition to its role as a buffering agent, sodium dihydrogen phosphate has other roles that are important for extending the shelf life of products and maintaining the health of human teeth and skin.

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