Stability of Sunscreen
Below is a formulation i made in the lab.
Octoocrylene - 4%
Ethylhexyl Methoxycinnamate- 7.5%
Benzophenone-3 - 1%
Ethylhexyl Salicylate - 5%
Uvinul A Plus - 2%
Hydroxyethyl cellulose- 0.2%
Preservative - 0.5%
The calculated SPF is 30, however after in vitro test the SPF value I got is only 7.
Could this be due to the instability of the formulation.
If yes, how can I improve on the stability?