Malvern Cosmetic Industry Particle Size Measurements

The cosmetic and personal care industry has an extremely diverse range of products. These include antiperspirants, hair sprays, toothpaste, facial products (lipstick, mascara, eye shadow etc.), nail varnish, emery boards, moisturizers (body lotions, hand creams) and exfoliants to name but a few. In all these products, particle size distribution and rheology are key indicators of its final performance. The shelf life (which will depend on the zeta potential and rheological properties) may also be of interest.

Sprays
Antiperspirants and hair sprays are classic examples in which the particle size distribution governs the performance of a product. If the particle size of an antiperspirant is too small it will not block the pores in the skin and not stop the user sweating. The hold of a hair spray (soft or firm) depends directly on the gel particle size produced by the can. It is especially important that there are no particles of a size small enough that could be inhaled by the user. The viscosity (flow) of the material under high shear rates (as it exits the orifice at high speeds) also helps determine its ability to form well dispersed droplets.

Toothpaste
Toothpaste generally consists of an abrasive material and a whitener, normally these are minerals such as calcium carbonate and titanium dioxide. The particle size distribution of these will determine the color of the toothpaste and how effective it is in plaque removal. Rheological properties will help determine mouth feel and how effective the extruded toothpaste will stay on the brush or flow into the bristles, in addition to how effective it will flow when brushed in the mouth.

Lipstick
The color density of lipstick is influenced by the type and particle size distribution of the pigments used. The degree of gloss or frosting is achieved by varying the particle size distribution – greater frosting is achieved by a wider particle size distribution. Color bleeding or feathering is influenced by the amount of fines in the product, which also affect the staying power. Rheological properties determine coverage on the lips and how well it will flow when pressed (at varying pressures) on the lips.

Mascara
Filaments (threads of silk) are present in some mascaras. They give body and added length to the eyelash. Agents are also added to hold the curl without flaking. Tight particle size control of the substrate helps the formulators to achieve these aims; a larger particle size distribution of the agents makes flaking more likely. Control of the rheology enables one to optimize the quantity of material delivered during application, as well as the proper thickness.

Eye Shadow
When formulating an eye shadow, you require a product that is permanent and in some cases the particle size can influence the degree of frosting. Generally a good eye shadow may be defined as one, which exhibits a fine particle size distribution. This means it is more likely to blend into the skin, be more durable and prevent creasing in the fold of the eyelid. Rheological properties help determine optimum deposition quantity and thickness.

Foundations, concealers and blushers
The particle size of a foundation should not be so small as to block up the pores but not so large that the fine lines in the face are accentuated. Particle size distributions and rheology are particularly important in the analysis of fumed silica (one of the major ingredients in soft gels and creams). The smaller the size, the greater the surface area and the less material required for the desired viscosity. If the particle size of a blusher is too large and rheological properties are not properly controlled, it will not spread well.

Moisturizers
Moisturizing products need to rapidly absorb into the skin. Liposomes are often used. The size of such products are generally less than 200nm.

Exfoliants and Emery Boards
These generally contain abrasive agents such as ground apricot kernel. A larger particle size distribution is required here in order to abrade the dead skin. In more sensitive areas of the body such as the face, a finer particle size is often used. The particle size distribution of the abrasive used in emery boards is also important, as the size will influence the degree of abrasiveness.

Nail Varnish
The particle size distribution influences the setting time and how chip proof and durable the nail varnish is. If the particle size is too large flaws will appear in the nail varnish commonly known as streaks. Proper control of the rheological properties will enable good leveling and coverage of brush marks, ensuring a higher quality appearance.