Sunscreen Formulation: DHHB Dissolution Issue

Sunscreen Formulation: DHHB Dissolution Issue

Dear User,

We understand you are experiencing difficulty dissolving DHHB in your sunscreen formulation using Homosalate, Oxybenzone, Octocrylene, DHHB, and Avobenzone, and you aim to achieve SPF 50+ and PPD greater than 30.

Based on the information provided by cosmeceutical7 and our product data, DHHB and Avobenzone are powdered sunscreen ingredients that require sufficient liquid solvents and heat to dissolve.

The issue of DHHB (and likely Avobenzone, which is also a powder) not dissolving is typically caused by the following main reasons:

1. Total amount of powdered sunscreens exceeds the solubility capacity of the oil phase solvents: The liquid sunscreens you are using (Homosalate, Oxybenzone, Octocrylene) act as solvents for powdered DHHB and Avobenzone. However, each solvent has a limited capacity to dissolve powders. If the combined amount of DHHB and Avobenzone is higher than what your blend of Homosalate, Oxybenzone, Octocrylene, and any other oils in your formula can dissolve, precipitation will occur, and they will not dissolve completely.

   • According to product information, DHHB is soluble up to approximately 36% in Homosalate and 39% in Octocrylene.
   • Avobenzone is soluble up to approximately 19% in Homosalate and 24% in Octocrylene.
   • You need to consider the total amount of DHHB and Avobenzone relative to the total amount of Homosalate, Oxybenzone, Octocrylene, and other oils/solvents in your complete formula to see if the proportion of powders is within the limit that the total solvents can dissolve.

2. Insufficient heat or heating time: Dissolving powdered sunscreens requires heat. It is generally recommended to use heat around 80-85 degrees Celsius and stir until completely dissolved. Avoid excessive heat or prolonged heating (e.g., DHHB should not exceed 80°C for more than 30 minutes) to prevent degradation.

Suggested Solutions and Recommendations:

• Check Sunscreen Proportions: Calculate the total amount of powdered sunscreens (DHHB + Avobenzone) and the total amount of liquid sunscreens (Homosalate + Oxybenzone + Octocrylene), as well as any other oils or emollients used in your formula. Consider increasing the proportion of liquid sunscreens that are good solvents, such as Homosalate and Octocrylene, to help increase the solubility of the powders.
• Use Appropriate Heat: Ensure that the dissolution step involves heating to approximately 80-85 degrees Celsius and continuous stirring until the powders are completely dissolved.
• Consider Regulatory Limits: In Thailand, each sunscreen ingredient has maximum allowed usage rates: DHHB up to 10%, Homosalate up to 10%, Oxybenzone up to 10%, Octocrylene up to 10%, Avobenzone up to 5%. Achieving SPF 50+ and PPD > 30 may require relatively high concentrations of sunscreens, which must not exceed these limits and must also be soluble in your formula.
• Achieving SPF 50+ and PPD > 30: Obtaining a PPD value greater than 30 typically requires high amounts of UVA filters, especially DHHB. At concentrations >7.5%, DHHB provides PA++++ (PPD > 16). To reach PPD > 30, you may need even higher amounts of DHHB or use it in combination with Avobenzone at appropriate levels (Avobenzone up to 5% provides PA+++). Using Oxybenzone and Octocrylene with Avobenzone helps improve Avobenzone's stability.
• Balance the Formula: Increasing the amount of liquid sunscreens to help dissolve powders may affect the texture of your formulation. You might need to consider using other oils or emollients that also aid in dissolution.

In summary, the dissolution problem arises when the amount of powdered sunscreens exceeds the capacity of the solvents in your formula, or if insufficient heat is applied. Try adjusting the ratio of liquid sunscreens relative to the powders and ensure you are using appropriate heat and mixing time for dissolution.