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Australian
Standard
Changes to the skin caused by UVA radiation -
unlike the acute UVB-induced damage - are due to a cumulative effect,
with damage occurring over a long period of time and therefore, difficult
to reproduce and measure experimentally in vivo. Unlike the definition
of the sun protection factor (SPF), there is a lack of an international
standard for the in vivo definition of the effect of UVA radiation.
There are various methods in use but their results are only partially
comparable with each other.
So far, there is only one standardized in vitro
measuring method in the world that is approved by a regulatory authority,
and that is the Australian Standard 2604:93. It allows for a reproducible
estimation of the reduction of UVA radiation brought about by a sunscreen
preparation. An exactly defined test procedure using a photometric
technique is employed. The result is a UVA protection value, expressed
as a percentage. Protection products that meet this strict standard
must absorb at least 90% of the UVA radiation.
Chemiluminescence method
This method, developed by Beiersdorf Skin Research,
demonstrates the antioxidant effect of skincare and protection products.
It is based on the principle that, when damaging free radicals, for
example UVA-induced oxygen radicals, are active, they emit photons
(light quanta). The number of photons emitted over a period of time
is a measure of the oxidative stress of the skin. On the other hand,
the reduction in photon emission through treatment with antioxidants
such as α-glucosylrutin and vitamin E is a measure of the protective
efficacy of these substances.
In order to induce the production of such reactive
(oxygen) species in the skin in a standardized way, a defined UVA
radiation dose (100 mJ/cm 2 skin) is used. If, after application of
a product, such a UVA-irradiated area of skin emits fewer photons
than an untreated or placebo-treated area, then the antioxidant effect
of the product has been demonstrated. The photons emitted from the
skin are measured with a highly sensitive light amplifier (photomultiplier)
and a photon-counting system UPE (Ultraweak Photon Emission) operated
in a completely darkened room.
COLIPA method (see also
SPF)
Comedogenicity
The term "comedogenicity" describes the tendency
of a topical preparation or ingredient to induce the formation of
sebum plugs (comedones) in the openings of the sebaceous glands. These
comedones can lead to inflammatory processes, which are visible in
the form of acne. They occur when an increased rate of sebum production
accompanies a simultaneous blockage of the sebaceous gland openings.
The closed sebaceous glands become infected by propionibacteria, which
produce porphyrin as a metabolite. With suitable light excitation,
this displays fluorescent properties which can be measured by imaging
techniques for early detection of acne caused by the use of cosmetic
products.
Conversely, this method can also be used to establish
the anti-comedogenic properties, i.e. the comedolytic activity, of
a skincare product, for example an anti-acne preparation.
Corneometry (see Skin
moisture)
D-Squames® * (see Skin
scaling)
* ® by Cuderm Corps., Dallas, Texas/USA
Elasticity test (see
Skin elasticity)
Evaporimetry (measurement of the
transepidermal water loss)
Evaporimetry is a method of measuring the transepidermal
water loss (TEWL). It is used as a parameter of the skin's barrier
function, where an increase in the measured value indicates an impaired
barrier function.
The transepidermal water loss is measured with
a special probe that alters its electrical properties as a function
of the water vapour pressure directly above the skin. As the measurement
can be strongly influenced by the activity of the sweat glands, the
measurements take place in a fully air conditioned room, which is
maintained at a constant temperature. A beneficial effect of skin
care is demonstrated by a lower measured value in treated than in
untreated areas.
Follicle biopsy
The skin surface biopsy technique is a simple,
reliable method for examining the stratum corneum, e.g. the individual,
interconnected corneocytes, pathological changes in the stratum corneum,
and the contents of the pilosebaceous follicles. To obtain material
for examination, a special adhesive, cyanoacrylate, is used. After
only a short time, this polymerises adhering firmly to the keratin
in the stratum corneum. After application onto the skin, a clean slide
is placed on top and pressure applied. After 20 - 30 seconds, the
slide is slowly removed, along with 3 - 6 layers of dead stratum corneum
cells. With a biopsy of sebaceous gland-rich areas of skin, follicles
and associated hairs are also removed. In skin conditions such as
acne vulgaris, the size of the funnel-shaped openings and the size
and composition of comedones can be examined in comparison with normal
skin.
Skin elasticity (elasticity test)
To measure skin elasticity, a measuring head
is placed on the area of skin of interest. A partial vacuum is created
with the help of a vacuum pump. The suction and release times are
specified and set before starting the measurement. The depth of penetration
(deformation) of the skin into the 2 millimetre wide measuring probe
is measured optically by means of a mirror and a light detector. The
time taken for the skin to return to its original state (recovery)
after release of the vacuum is quicker or slower according to the
skin condition. The measure of skin elasticity is given by the following
formulas:
Skin moisture (corneometry)
The water content of the horny layer is important
as a protective factor (barrier function) but also plays an important
role in the cosmetic appearance of the skin. If it is too low, the
skin becomes dry and chapped and cannot fulfil its barrier function.
The amount of moisture in the horny layer is determined by corneometry.
As a measuring probe, a plate capacitor is used which builds up an
electrical field at its edges.
The properties of this electrical field change
in accordance with the water content of the en-vironment through which
it moves. The plate capacitor is separated from the skin by an extremely
thin film which prevents ion-containing skin surface water from causing
a short circuit between the capacitor plates. The measurements take
place in a fully air conditioned room, which is maintained at a constant
temperature. This is because the measurement can be strongly influenced
by the activity of the sweat glands.
Skin smoothness and skin roughness
(profilometry, microtopography/skin micro-topography, see also
Replica method)
If the skin is well supplied with skincare substances,
the skin moisture content improves, the barrier function is supported
and skin roughness (scaling) is reduced. Together these lead to a
smoothing of the skin's surface that can be observed in the micrometre
region (1 mm equals 1000 µm). In this manner the smoothness of the
skin's surface can be used as a "skin rejuvenation" parameter, as
the skin roughness in the micrometre region is related to the age
of the skin. The skin's microstructure is measured - as with the pick-up
of a record player - with a very fine needle that passes over the
skin relief, following it exactly with up and down movements. In this
manner the success of a smoothing treatment can be demonstrated to
within a few micrometres.
However, the skin pulsates, and such a delicate
measurement cannot take place directly on the skin's surface. For
this reason, an exact replica of the skin's surface profile is made
using a silicone/dental-impression mass from which the measurements
are taken and described, according to German industrial standards.
With the aid of an imaging technique they are repro-duced in 3D format.
Thus the different surface parameters, such as roughness or moderately
deep wrinkles, can be measured and compared with each other. The data
for the replicas are obtained, stored and computed automatically.
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By means of 3D reconstruction,
wrinkle depths can be depicted: warm colours (red, yellow) show large
depths of wrinkles and cold colours (green, blue) small wrinkle depths. |
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Skin surface lipids (sebumetry)
The amount of skin surface lipids, which mostly originate from sebum,
is measured with the help of a sebumeter. The amount of sebum on the
skin's surface differs according to skin region and depends either
on the density of the sebaceous glands, or their level of activity.
This peaks in puberty and then continually declines. A low level of
skin lipids can - especially in later years - lead to increasingly
dry skin. The skin surface lipids can be quantitatively measured:
The sensor of the measuring apparatus is placed on the skin. An opaque
film on the sensor tip soaks up the sebum. This film becomes more
or less transparent, depending on the amount of sebum ("grease-proof
paper effect"). This transparency is measured and expressed as a numerical
value.
Skin roughness (profilometry,
see Skin smoothness and skin roughness)
Skin regeneration (see Corneocyte
size, measurement of ~)
Skin scaling (D-Squames® *)
* ® by Cuderm Corps., Dallas, Texas/USA
The epidermis of young skin is continuously renewed by the constant
production of keratino-cytes, their differentiation/cornification
and desquamation every 28 days. When a disruption occurs, such as
by enzyme-activity controlled desquamation, large corneocyte aggregates
are formed, which appear as scaling to human eyes. These skin scales
are composed of horny cells and consist mostly of keratin, in other
words amino acids.
When the corneocyte aggregates are removed with a special adhesive
film (D-Squames ® *), the degree of scaling can be measured and the
effect of a treatment assessed. This is done by exposing the film
to UV light: As some amino acids in the skin scales fluoresce, the
intensity of the fluorescence on the standardized adhesive film as
depicted by image analysis gives an approximate indication of the
amount of skin scales present.
Corneocyte size, measurement of
~ (skin regeneration)
The corneocyte size is an indication of the epidermal turnover, i.e.
the regenerative capacity of the skin. The faster the turnover, the
smaller the size of the horny cells (corneocytes). In humans there
is a very clear age dependence of the corneocyte area (CA): There
is an approximately linear increase from birth to old age on parts
of the body exposed to little or no UV radiation. After treating the
skin for six to eight weeks with active preparations, the first statistically
significant changes in the size of corneocytes flaking off from the
skin can be detected. Agents that stimulate epidermal regeneration
reduce the corneocyte size. If a preparation inhibits or calms the
(primary hyperproliferative, e.g. atopic) skin, the corneocyte size
will increase. Corneocytes are removed from the skin surface with
an adhesive film in a standardized procedure and measured on a slide
by means of a microscope-coupled imaging system. Then the results
are compared with those of an untreated skin area.
Sun protection factor (SPF)
The determination of the sun protection factor (SPF) in Europe follows
the COLIPA standard of the European Cosmetic, Toiletry and Perfumery
Association. It stipulates the amount of protection a sunscreen should
provide from UVB radiation. UVB radiation is the main cause of sunburn.
Moreover, it possesses immunosuppressive and cell damaging properties
that after chronic exposure can lead to skin cancer (basaliomas, spinaliomas).Various
UV filters and UV filter systems/combinations are used in order to
provide optimum protection. The minimal erythema dose (MED) is the
measurement of the amount of UVB radiation that is needed to induce
a barely noticeable reddening (erythema). The SPF can be calculated
using the following formula:
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MED on protected skin |
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MEDp |
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=
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SPF
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MED on unprotected skin |
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MEDu |
A
test begins by determining the individual UV sensitivity of the
test participant by exposing an unprotected skin area on the back.
The radiation sources are solar simulators, most equipped with xenon
lamps: their spectrum is sun-like but of a higher intensity and
therefore a shorter radiation period is possible. Approximately
20 hours after exposure to varying intensities, the MEDu is determined
by visual assessment of the erythemas in six skin areas.
For the actual SPF determination, test areas are marked out on the
participant's back for the application of the sunscreen preparation.
Every product area has a neighbouring untreated control area assigned
to it. The intensity of the exposure is determined according to
skin sensitivity and the expected sun protection factor. After approximately
20 hours the MEDu and MEDp are visually assessed. The resulting
sun protection factor gives the average increase in the individual
time periods needed to produce an erythema after the application
of the sun-screen.
SPF:
COLIPA
method
Since 1997, the COLIPA method has been the one used throughout Europe
to determine the sun protection factor (UVB protection) of sunscreens.
The test method is standardized and regulated. The radiation range
and the output of the sun simulator used for testing are defined
exactly. The amount applied and mode of product application are
also laid down precisely. The test method is independent of skin
type or the age of the test subjects. These precise specifications
mean that statistically significant sunscreen testing can take place
with only ten volunteers. The COLIPA method is a method that yields
reproducible results with a high degree of reliability.
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Microtopography (see Skin
smoothness and skin roughness)
Surface hydrometry
Surface hydrometry is the measuring of the
water content of the surface of the horny layer.
OECD method (biodegradability)
Under the 1977 Statutory Order, the OECD confirmatory
test and the OECD screening test, in combination with the MBAS (methylene
blue active substance = a group-specific method to detect anionic
surfactants) or BiAS (bismith active substance = a group-specific
method to detect non-anionic surfactants), have been designated
as the methods for testing the biodegradability of anionic and non-anionic
surfactants.
The OECD screening test is known as a die-away
test, in which the reduction in a preset concentration of a substrate
over time is followed directly or indirectly. In the die-away test,
the introduction of sewage into a river is simulated by the use
of a suspension with a low density of bacteria. The 19-day test
interprets the primary degradability of the substrate. A reduction
of more than 80% MBAS or BiAS is considered sufficient. With the
28-day modified OECD screening test, the end-degradability of the
test substance is defined. A reduction in organically bound carbon
(DOC = dissolved organic carbon) of more than 70% is regarded as
a criterion of ready biodegradability. The OECD confirmatory test
is a continuous test method, in which a treatment plant model with
a high density of bacteria is simulated.
The tested surfactant is regarded as biodegradable
if there is a reduction of more than 80% MBAS or BiAS.
Patch test
This test serves to establish the topical safety
of a preparation. The test substance is applied to a plaster measuring
approximately one square centimetre and stuck to healthy skin for
24 hours. After removal of the test plaster, the skin area in question
is evaluated after 10 minutes, 12 and 24 hours. In a repetitive
insult patch test the procedure is repeated five more times at intervals
of 48 hours and again 10 days later.
Photoallergy
test (see also Photopatch test)
A photoallergic reaction occurs when light-sensitive
substances in the skin are activated by exposure to UVA radiation.
That means that the substance concerned has been transformed into
a higher energy, more reactive which can cause damage to surrounding
tissue. This is manifested to as either a phototoxic or photoallergic
reaction.
To diagnose this condition, what is known as
a photopatch test is performed: A photoallergic reaction shows only
a limited dose dependence, is usually eczematous and lasts longer
than a phototoxic reaction for example. It is based on an immune
reaction to an allergen generated by the light-induced reaction.
Photopatch test
The photopatch test is used to detect
the presence of photoallergic or phototoxic reactions. The test
substances are placed in two parallel series on the skin of the
back by means of test plaster and over-laid with a black light-proof
film. After 24 hours one of the plaster series is removed and the
skin is irradiated with UV light (the minimal erythema dose). After
24 hours both test areas are inspected. In the case of phototoxic
or allergic reactions the exposed skin test fields are positive,
the unexposed negative. Photoallergic reactions can also spread
into neighbouring areas that have not been exposed.
Photoprovocation test
In the photoprovocation test, also known as
phototesting, a skin area is inspected for a reduced erythema threshold
or persistance of erythema after exposure to UVA or UVB radiation.
The light-induced erythema is examined for skin lesions that are
typical of photodermatoses such as polymorphic light eruptions (PLE;
papules, weals, blisters). In this manner, the method is also used
in general diagnostics.
Phototoxicity test (see also
Photopatch test, Photoallergy test)
Unlike photoallergic reactions, phototoxic
reactions are dose-dependent, confined to the ir-radiated area and
manifest themselves as sunburn-like symptoms. Thus the skin reacts
under UVA radiation to a single contact with a certain substance,
such as bergamot oil (berloque dermatitis) or substances found in
the cow parsnip (meadow (grass) dermatitis), with a photo-toxic
reaction. Testing for phototoxicity is done with the photopatch
test.
Profilometry (see also Skin
smoothness and skin roughness)
Profilometry is a method for determining skin
roughness. A silicone impression mass is used to make an impression
of a specified skin area and then measured. The values obtained
reflect the skin smoothing properties of a topical preparation.
Repetitive insult patch test
(RIPT) (see Patch test)
Replica method (see also Skin
smoothness and skin roughness)
The replica method is a reproducible measuring
technique that studies and documents the topography of the skin's
surface.
Suction blister test
Suction blisters are an accepted model for
testing a number of hypotheses relating to skin physiology and pharmacology.
This test is also used as a standardized wound-healing model for
objective assessment of the influence of active ingredients such
as dexpanthenol on epithelial regeneration. In this test, intra-epidermal
blisters representing precisely defined defects are produced artificially
by negative pressure. In addition to the course of re-epithelialisation,
the constituents of the blister cover and the fluid in the blister
can be analysed. Measurement of transepidermal water loss (TEWL)
is a suitable parameter for recording the degree of re-epithelialisation.
SDS test
The SDS test records and evaluates skin reactions
provoked by the application of sodium lauryl sulphate (sodium dodecyl
sulphate = SDS) as a standard irritant, e.g. on the fore-arm. The
degree of skin irritation, e.g. before and after product use, is
evaluated from the redness of the irritated area of skin, measurement
of skin colour (chromametry) and measurement of transepidermal water
loss.
Sebumetry (see
Skin surface lipids)
Stinging test (lactic acid stinging
test)
First published by Frosch and Kligman in 1977,
the "lactic acid stinging test" is used to identify people with
hyperirritable or "sensitive" skin, also called stingers. This test
can detect neurosensory problems such as stinging, burning and itching
related to the application of various skincare products, even if
there is no disease or clinical symptoms of irritation present.
"Stinging" refers to the sensation experienced
by sensitive people to the topical application of a 10% concentration
of lactic acid that normally appears after a few minutes. After
approximately 3 to 5 minutes the reaction reaches its peak and then
declines over the next 15 to 20 minutes. In especially sensitive
persons, a light erythema can appear.
A stinging test is carried out under standardized
conditions (patch, chamber test) and in a defined environment (room
temperature and humidity, time of year). The lactic acid is applied
to the nasolabial area of one side of the face. The test participant
must differentiate between the sensations of burning, stinging and
itching. For the two weeks leading up to the test, no cleansing
or skincare products may be used. In order to exclude a placebo
effect, the test participant is tested one week later with a water-soaked
patch as a placebo.
Stinging lactic acid conditioning test
The purpose of the test is to study the skin-protecting
efficacy of medicated facial skin-care products. Test subjects with
sensitive, easily irritated skin have a cream containing no active
ingredients (placebo) applied to the nasolabial region of both sides
of their face for one week. Then, in the 1st stinging test, 10%
lactic acid is applied to the nasolabial region of both sides of
the face and the skin reactions and subjective sensations (e.g.
burning, stinging, itching) are observed and documented. In the
second week, a placebo is applied to the nasolabial region of one
side of the face, and a cream containing the test ingredient (active
ingredient) to the other side. In the 2nd stinging test, a 10% lactic
acid solution is again applied, and the skin reactions after pre-treatment
with the active ingredient or placebo recorded.
UVA protection (see also Australian
Standard)
A whole host of methods for determining the
UVA protection factor have been published. However, what have been
lacking to date are standard international in vivo methods. Australian
Standard 2604:93 is an in vitro method and to date the only official
measurement method that enables the reduction in UVA radiation achieved
by sunscreens to be reproducibly estimated. This method defines
a test set-up that determines the percentage UVA protection value
using a photometric method. Only with 90% UVA filtration is the
standard deemed met.
UVB
protection (see also Sun protection factor)
The sun protection factor found on the packages
of sunscreen products applies only to the protection afforded against
UVB radiation. This value indicates how much longer a person can
stay in the sun before a barely noticeable erythema becomes apparent
when the skin is protected compared to when it is not.
In the past, the
UVB sun protection factor has been measured according to various
standarized methods such as the US/FDA standard and the DIN 67501
Standard. This meant that the UVB sun protection factor for one
and the same sunscreen product could vary depending on the test
method used. The current COLIPA standard is a standarized method
for measuring the UVB sun protection factor that has been effective
throughout Europe since 1997. This has the advantage that SPF values
reported by different manufactures are comparable. The SPF value
stated on the packaging of Eucerin ® Sun Products were measured
according to the COLIPA method.
Water loss, transepidermal
(see Evaporimetry)
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