SUN CARE
2% aqueous spherical silica gels showed no in vitro SPF. Silica gels do two important things to
promote SPF boosting. Firstly, they form a thick and uniform film on the skin because of their large particle size. This enhances the dispersion of the mineral actives throughout the film. Secondly, silica gels are porous, so they
excel at scattering light. As UV light passes through the film of product on the skin, the porosity of the silica gels increases the pathlength and causes it to scatter in all directions. These two factors prevent UV light from
reaching the skin and promote more UV light reflection from the skin, raising the SPF of the inorganic sunscreen up to 200%. As a bonus, the pores of the silica gels are excellent absorbers of oil and sebum, so the greasy/slimy feeling disappears.
Advantages of silica gels Microspherical silica gels are made from silicon dioxide, a natural material. They are an ideal replacement for traditional SPF boosters like waxes and microbeads, and they provide more SPF boost and better aesthetics than hollow- sphere particles. Porous microspherical silica gels with a 3 µm
particle size boost SPF and dramatically improve aesthetics of W/O formulations. Their 700 m2
/g
surface area is higher than most microbeads, and they do not deform like plastic beads. The spherical silica gels also provide
a silky-smooth feel as a result of their absorption properties. Because of the porosity of the spheres, they also provide a ‘soft-focus effect’ that blurs the appearance of wrinkles. Tests show that adding just 2% of spherical
silica gels to a W/O emulsion sunscreen can transform the aesthetics from ‘acceptable’ to ‘outstanding’, rivaling O/W emulsions. The following characteristics provide maximum light scattering:
Sunscreen product
Skin Skin
Figure 1: As UV light passes through the film of the sunscreen product on the skin, the porosity of the silica gels increases the pathlength and causes it to scatter, promoting UV light reflection from the skin
PRESSURE FINGER DEFORMED
PRESSURE FINGER
Sunlight
55
Light-scattering silica
UV scattering agent UV absorber or
SKIN PLASTIC BEADS
SKIN SOLESPHERE SILICA MICROSPHERES
Figure 2: Silica gels are harder than plastic microbeads, so they retain their spherical shape and roll on easier, improving spreadability on the skin
■ Mean particle size of 3,000 nm ■ Specific surface area of 700 m2
/g
■ Pore volume 2 mL/g ■ Pore diameter of 11 nm Silica gels have large particle sizes
compared with traditional/conventional SPF-boosting additives like waxes, microbeads and powders. Large particles
lead to thicker films that spread more evenly on the skin. Silica gels are also near-perfect spheres
and harder than plastic microbeads, so they do not deform when pressed with the fingers. They retain their spherical shape, so they roll on easier, improving spreadability on the skin.
www.personalcaremagazine.com
October 2022 PERSONAL CARE
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