Synergy effects between organic and inorganic UV filters in sunscreens

Abstract

The influence of the synergy effects between organic and inorganic UV filter substances on the sun protection factor (SPF) of topically applied sunscreen formulations is investigated. The medium is considered to have reflection, absorption, and scattering properties. The distribution of photons in this medium is investigated by Monte Carlo calculation. Typical optical parameters of the skin and substances are used to characterize the synergy effect. The results of the model calculation are checked by in vitro and in vivo measurements investigating the influence of different types of scattering microparticles on the absorption efficacy of topically applied formulations. It is found that the inorganic filter substances act as scattering microparticles in the upper skin layers. They increase the optical pathway of the photons in the topically applied absorbing formulation also localized there. In this way, more photons are absorbed, increasing the SPF. The results obtained are important for the optimization of the SPF of sunscreen formulation containing organic and inorganic UV-filter components.

Effect of size of TiO[sub 2] nanoparticles embedded into stratum corneum on ultraviolet-A and ultraviolet-B sun-blocking properties of the skin

“…This phenomenon of synergy was investigated experimentally also for some kinds of scattering microparticles increasing the absorption of inorganic UV filters. 39 Absorption of 400-nm light induced by 25-to 40-nm particles is weak, correlating with a low magnitude of the extinction ͑scattering͒ curve, as shown in Fig. 2͑a͒, that results in weak interaction between particles and photons.…”

Methods for the Evaluation of the Protective Efficacy of Sunscreen Products

“…A homogeneous spreading of the sunscreen from the application area was also observed into the neighboring nontreated skin areas. Homogeneous spreading represents a prerequisite for a good quality efficacy of a sunscreen product, which is determined by the homogeneity of the distribution of the sunscreen on the skin, as well as by the absorption properties of the UV filter substances and by the annihilation of the absorbed photon energy in the skin [36,37]. With a well-balanced filter combination entailing synergetic effects and the homogeneous distribution of these filters on the skin, a high protective efficacy can be achieved for the investigated sunscreen Anthelios XL Fluide Extreme (SPF 50+), using a small amount of filter substances.…”

Sunscreens: An overview and update

“…Organic and inorganic filters may also act synergistically to increase SPF. 37 Inorganic agents scatter UV light, increasing the photons' optical pathways and enhancing subsequent absorption by organic agents. 37 …”