Beauty Forum Feb23 - Flipbook - Page 41
e for the skin penetration
What molecular weights do cosmetic
As cosmetic ingredients, very diverse molecules
are used in terms of their size - from small ones
(acids, vitamins), to polymers (hyaluronic acid),
peptides or proteins.
Let us remember that many cosmetic ingredients
(e.g. extracts, oils, hydrolates) are complex
mixtures that include many chemical compounds.
Therefore, the molecular weight of the extract or
essential oil cannot be determined.
When does the 500 Da rule not work?
weight because this data is more readily available
and unambiguous (size measurements are much
more complex and difficult to interpret).
500 Da Rule
In 2000, two scientists from the University of
Amsterdam proposed to determine the possibility of
absorption through the skin of the so-called 500
Dalton rule. The rule states that a molecule must
be below 500 Da to be able to penetrate the skin.
They justified this with three arguments:
Virtually all known contact allergens are below 500
Da. A molecule that is in contact with the skin, but
is not able to penetrate it in adequate amounts,
cannot be an allergenic agent. For example,
fragrance allergens (eugenol, geraniol, etc.) have a
size of approx. 150-200 Da.
The most commonly used medicinal substances on
the skin are below 500 Da (e.g. topical
corticosteroids are around 400-500 Da).
All substances in transdermal patches are below
500 Da (e.g. nicotine approx. 160 Da). Since then,
this principle has become a permanent feature in
pharmacy, toxicology, and also in the sciences
related to cosmetics as it is commonly used to
predict skin absorption and describe the safety of
First of all, when the skin barrier is damaged,
whether as a result of injury or disease (e.g. atopic
dermatitis, psoriasis). Then the ability to penetrate
the skin of larger particles also increases. There
was also a publication in which an exception to this
rule was shown - penetration was observed for a
protein of 6000 Da.
Particle size is an important, but not the only,
determinant of skin permeation. Also, the mere fact
that a particle penetrates the skin is not an
indication of its effect - there are cosmetic
ingredients that do not penetrate, but perfectly fulfil
their care role. And most of the so-called active
ingredients are small, penetrating particles.
Bos et al., The 500 Dalton rule for the skin penetration of chemical
compounds and drugs, 2000, Experimental Dermatology, 9, 165169
Environmental Health Criteria 235 Dermal Absorption link
Schaefer et al., Skin Penetration link
Essendoubi et al., Human skin penetration of hyaluronic acid of
different molecular weights as probed by Raman spectroscopy,
2016, Skin Research and Technology, 22, 55-62 link
The 500 Dalton Rule of Dermal Penetration and Cosmetic
Science, [09.06.2021] link 1