Each of the skin’s layers, including
the makeup, transmits, absorbs and
reflects part of the light that falls on
it. The reflected light exits through a
different point from where it entered.
These subsurface scattering effects allow
us to distinguish living humans from
mannequins and crash-test dummies;
computer graphics specialists use sophisticated modeling algorithms to emulate
this kind of light scattering when they
develop realistic humanoid characters for
Cosmetic scientists, however, must
work with micron-sized particles of real
material instead of pixels. Following the
demand of modern customers for the
“natural” look in makeup, they have been
creating composite particles that scatter
light, blurring skin imperfections instead
of covering them with opaque pigments.
Researchers are also seeking new ways to
add iridescence to cosmetics by borrowing
ideas from naturally occurring substances
and photonic crystal technology.
The basics: pigments,
dyes and lakes
Pigments are inorganic, insoluble materials that are ground into fine particles and
suspended in liquid. Two of the most
common cosmetic ingredients are simple
mineral pigments: iron oxide (either
FeO, which is black, or Fe2O3, which
is reddish-brown) and titanium dioxide
(TiO2, which is white).
To impart color to the skin, most
pigment particles should be around 3 to
5 µm in diameter, said Nick Morante, an
independent color consultant who operates a cosmetic formulation laboratory in
Holbrook, N. Y. (U.S.A.). Although zinc
oxide and titanium dioxide are both white
pigments, when they are ground down
to particle diameters of less than 1 µm,
they lose their color value but still act as
a sunscreen by absorbing, reflecting and
scattering ultraviolet light. The product
may look white when coming out of the
bottle or tube, but once the user spreads it
on his or her skin, it looks transparent.
Dyes, which are soluble in liquids,
are mainly used in cosmetics in the form
demand of modern
customers for the
“natural” look in
scientists have been
particles that scatter
light, blurring skin
of covering them with
[ Layers of the epidermis ]
Makeup is applied to the stratum
corneum, the outermost layer.
of “lake pigments,” which are a sort of
hybrid between dyes and pigments. To
make a lake, the dye is precipitated onto
the surface of an inert insoluble binder,
such as aluminum oxide (alumina) or
calcium sulfate. The process makes it
easier to incorporate liquid dye colors
into dry or waxy cosmetic products.
In the United States, the Food and
Drug Administration (FDA) regulates
the coloring agents that go into cosmetics. There are lots of unregulated ingredients that manufacturers can use so long
as they are generally regarded as safe.
However, colors are controlled because
they have a poisonous history.
Before the 20th century, cosmetic
colors could be downright toxic. For
example, noble ladies of the 16th century whitened their skin with Venetian
ceruse, a mixture of mercury and lead.
Arsenic oxide was used as a white face
powder in the 18th and 19th centuries.
Kohl, a nearly black eye makeup known
since ancient Egypt, was originally
made with ground-up galena, which is
Nowadays, the cosmetics industry bends over backwards to ensure
safety and keep public confidence in its
products, said Robert Y. Lochhead, a
professor of polymer science at the University of Southern Mississippi (U.S.A.).
Lochhead serves as the 2010 president of
the Society of Cosmetic Chemists, a U.S.
Foundation: the look
and the feel
All ingredients of each cosmetic product
must interact well with each other. If
pigments don’t mix easily with the noncoloring components, the product might
cover the skin unevenly, wear off quickly
or feel uncomfortable on the face.
Foundations are the flesh-toned
substances that cosmetic users apply all
over their face to even out skin tone and
de-emphasize fine wrinkles. The first
mass-market foundation, Max Factor
& Company’s Pan-Cake, debuted in
the late 1930s. It consisted of pigments
mixed with a base of talc, or hydrated
magnesium silicate, and the wearer