Sunscreen Formulation: Achieving SPF 40-50 with Low Titanium Dioxide and Understanding Synergistic Effects

Asked by: malawadee On: October 18, 2014 Product Type: Cosmetics

Question

Based on the principles of sunscreen formulation, specifically using physical sunscreens like Zinc Oxide and Titanium Dioxide:

  1. What percentage combination of physical sunscreens is needed to achieve SPF 40-50, given the constraint that Titanium Dioxide must be less than 5%?
  2. When using a combination such as 20% Zinc Oxide and 5% Titanium Dioxide, what level of white cast or brightening effect should be expected?
  3. Could you explain why the stand-alone SPF value for 1% Zinc Oxide was updated from an estimated 2.5 to a new standard value of 1.5?

Answer

Based on the discussion provided:

Regarding the percentage of physical sunscreens needed for SPF 40-50 with Titanium Dioxide under 5%:

  • Achieving SPF 40-50 is possible with a combination of Zinc Oxide and Titanium Dioxide.
  • The discussion suggests using a high percentage of Zinc Oxide (up to the maximum allowed, 25%) combined with a lower percentage of Titanium Dioxide (like 5%).
  • The example mentioned (Neutrogena with 4.9% Titanium Dioxide and 4.7% Zinc Oxide achieving SPF >60) shows that these ingredients work synergistically, meaning the combined SPF is higher than just adding their individual stand-alone values.
  • Therefore, a combination like 20% Zinc Oxide and 5% Titanium Dioxide is very likely to achieve SPF 40-50 or even higher due to this synergistic effect.

Regarding white cast with 20% Zinc Oxide and 5% Titanium Dioxide:

  • Keeping Titanium Dioxide at 5% helps minimize the white cast compared to using higher percentages. However, 5% Titanium Dioxide might still cause some degree of white cast or a brightening effect on the skin.
  • Zinc Oxide, even at 20%, is generally less likely to cause a severe white cast compared to Titanium Dioxide at higher concentrations, although it might have a slight sheen.
  • The combination will likely result in some level of white cast, but it should be less pronounced than formulations with higher Titanium Dioxide content.

Regarding why the SPF value for 1% Zinc Oxide decreased from 2.5 to 1.5:

  • The staff explained that the previous value (2.5) was an estimate based on typical market formulations where Zinc Oxide is used alongside other sunscreens, leading to a synergistic effect that boosts the overall SPF.
  • The new value (1.5) is the "stand-alone" value, which represents the minimum SPF achieved when using Zinc Oxide by itself. This provides a consistent, minimum standard value for the ingredient.

Tags

Broad-spectrum Efficacy Ingredient Standard Sun Protection Sunscreen Formulation White Cast Reduction