Comparative Analysis of Phytic Acid (Sodium Phytate) and EDTA as Chelating Agents in Cosmetics

1. Functional Differences

(1) Chelating Ability

1. Phytic Acid (Sodium Phytate) : The molecular structure of phytic acid contains 6 phosphate groups, which endow it with strong metal ion chelating ability, especially high affinity for metal ions such as Fe³⁺ and Cu²⁺. In cosmetic systems, these metal ions often act as catalysts for oxidation reactions, accelerating the oxidative rancidity of oils and causing discoloration and deterioration of products. By combining closely with them, phytic acid (sodium phytate) forms stable and complex-structured complexes, effectively preventing metal ions from participating in redox reactions, thus significantly extending the shelf life of products. For example, in vegetable oil-based cosmetics, adding an appropriate amount of phytic acid (sodium phytate) can obviously delay the odor and color changes caused by oil oxidation. Its chelating effect can be maintained in a wide pH range, providing greater flexibility for cosmetic formulation design.
2. EDTA : EDTA can form stable chelates with almost all common metal ions, such as Ca²⁺, Mg²⁺, and Pb²⁺, with an extremely wide chelating range. In cleansing cosmetics, it can effectively chelate calcium and magnesium ions in hard water, preventing these ions from combining with surfactants to form precipitates, which greatly improves the cleaning performance and foam stability of products in hard water environments. However, the excessive chelating effect of EDTA may also bring negative impacts. It may indiscriminately chelate some beneficial mineral ions needed by the skin itself, such as calcium and zinc. Over time, this may interfere with the normal physiological metabolism of the skin.

(2) Antioxidant Property

1. Phytic Acid (Sodium Phytate) : Phytic acid (sodium phytate) has both direct and indirect antioxidant capabilities. Indirectly, by chelating metal ions with catalytic activity, it cuts off the source of free radicals and inhibits free radical initiation processes such as the Fenton reaction. Directly, it can provide hydrogen atoms to free radicals, converting free radicals into stable structures, while itself forms a relatively stable free radical intermediate. At the same time, phytic acid (sodium phytate) can also have a synergistic effect with classic antioxidants such as vitamin C and vitamin E, stabilizing their structures and extending the action time of the antioxidant network. Research data shows that a 0.5% mass fraction sodium phytate solution has a DPPH free radical scavenging rate of over 80%, while the scavenging rate of BHT (Butylated Hydroxytoluene) at the same concentration is only 65%. In anti-aging and sunscreen cosmetics, phytic acid (sodium phytate) can effectively resist oxidative stress induced by factors such as ultraviolet rays and environmental pollution, protect the DNA, proteins, and lipids of skin cells from free radical attacks, and delay the skin aging process.
2. EDTA : In cosmetic systems, EDTA mainly functions to maintain the stability of the formulation by chelating metal ions and reduce the interference of metal ions on the system. However, it itself has no obvious antioxidant active groups, and its direct contribution in terms of antioxidant properties is relatively limited.

(3) Other Additional Functions

1. Phytic Acid (Sodium Phytate) :

   • Whitening and Spot Lightening : Phytic acid (sodium phytate) has a high affinity for copper ions in the active center of tyrosinase. It can bind closely to copper ions, inhibiting the activity of tyrosinase, thereby reducing the synthesis of melanin. Its half-inhibitory concentration IC₅₀ for tyrosinase is approximately 0.8 mM. In addition, phytic acid (sodium phytate) can also inhibit melanin production at the gene regulation level by reducing the expression of MITF (Microphthalmia-Associated Transcription Factor) induced by UVB. Clinical experiments have shown that after 8 weeks of combined use with niacinamide, the area of spots decreased by 37%, which is significantly better than the 25% reduction in the group using niacinamide alone.
   • Soothing and Anti-Inflammatory : Inflammation is an important inducement of skin problems such as aging and sensitivity. Phytic acid (sodium phytate) can reduce the release of pro-inflammatory factors such as IL-6 and TNF-α by down-regulating the expression of inflammation-related genes such as NF-κB and COX-2, thereby alleviating skin inflammatory reactions. For skin inflammatory problems such as sensitive skin and rosacea, adding 0.1 – 0.3% phytic acid (sodium phytate) to cosmetics can effectively reduce skin discomfort symptoms such as redness and itching.
   • Gentle Exfoliation : Phytic acid has a certain acidity, which can gently dissolve the connecting substances between keratinocytes in the stratum corneum, promoting the natural shedding of aged keratinocytes, accelerating skin metabolism, and making the skin surface smoother and more delicate. Compared with exfoliating ingredients such as fruit acids, phytic acid has a milder effect and is more suitable for sensitive skin.
   • Oral Care : In oral care products, phytic acid (sodium phytate) can chelate multivalent cations in the oral environment, such as calcium and magnesium ions, inhibit the dissolution of calcium phosphate, and effectively prevent the formation of dental caries. At the same time, it can also combine with metal ions in tooth stains and dental plaque to clean teeth and remove smoke stains, so it is often used in the formulation of toothpaste, mouthwash, and other products.
2. EDTA : In cosmetics, the main function of EDTA is centered on chelating metal ions. Although it can assist in bacteriostasis and enhance the effect of some preservatives, it itself does not have direct skin-improving functions such as whitening, anti-inflammatory, and exfoliation.

2. Differences in Application Environments

1. Phytic Acid : Phytic acid is an acidic substance. It has stable chemical properties in an acidic environment and can give full play to its chelating and other physiological activities. It works best in cosmetic formulations with a pH of 5.5 – 7. In acidic products such as whitening serums and toners, phytic acid can not only effectively chelate metal ions and maintain product stability but also use its acidic characteristics for gentle exfoliation, synergistically promoting whitening effects.
2. Sodium Phytate : Sodium phytate is alkaline and suitable for alkaline cosmetic systems. In an alkaline environment, sodium phytate can maintain its structural integrity, and its chelating groups are fully exposed, enabling efficient chelation reactions with metal ions. In alkaline cosmetics such as soap-based cleansing products, sodium phytate acts as a chelating agent, which can prevent the impact of metal ions on the soap base and improve product quality.
3. EDTA (Taking the Commonly Used Disodium EDTA as an Example) : Disodium EDTA is weakly acidic. It can exist stably and exert good chelating effects within the common pH range of 4 – 8 in cosmetics. Its wide adaptability to the pH value of the system is one of the key factors for its large-scale application in various cosmetics.

3. Comparison of Safety Performance

1. Phytic Acid (Sodium Phytate) : Phytic acid (sodium phytate) is derived from plants and is a naturally extracted ingredient. The median lethal dose LD50 of phytic acid for oral administration in mice is as high as 4192 mg/kg body weight, which is much lower in toxicity than table salt (the LD50 of table salt is 400 mg/kg), indicating extremely high safety. In the human body, phytic acid can be gradually hydrolyzed into inositol and phospholipids. Inositol has a certain anti-aging effect, and phospholipids are important components of human cells. Phytic acid also has the ability to relieve lead poisoning and can be used as a heavy metal antidote. In cosmetic applications, phytic acid (sodium phytate) has minimal irritation to the skin, which is particularly in line with the needs of consumers who pursue natural and gentle skincare concepts.
2. EDTA : EDTA and its sodium salts have a certain level of safety in cosmetics, and their addition amount is usually controlled at 0.05 – 0.2%. Due to its wide chelating range, in the complex skin microenvironment, it may excessively chelate beneficial metal ions required by the skin itself. With long-term and frequent use, there is a theoretical potential risk of interfering with the balance of the skin microecology. In eye cosmetics and other products that are extremely sensitive to the content of metal ions, the use of EDTA requires more careful evaluation to avoid adverse effects on the delicate skin around the eyes.