| h y d r o x y
. a c i d s |
|
|
|
t h e d a
y t o d a y b e a u t y
a n t i a g i n g s e r i e s
DayToDayBeauty
is undertaking as a public service to our readers a systematic
and comprehensive review of the topic of antiaging
agents and their use both in personal care
products and as prescription items if so available. We
review the latest evidence concerning
the most effective agents and products, provide guidance
on their optimal use and proper application, and discuss
any warnings or cautions that may be relevant.
In Part 1 of this series (May
2004), we discussed the world of Vitamin A
and its derivatives (retinoids), both natural and
synthetic. In this newsletter (part 2, September 2004),
we review alpha hydroxy acid (AHA) and related
agents. In the next part of this series (part 3) we review
antioxidants (including vitamins), moisturizers,
and several other recently introduced agents, including
the controversial Botox. In
the concluding part of the antigaing series (part 4) we
summarize all our previous research and provide specific
and practical guidelines for the best effective treatment
of aging skin.
Readers may subscribe (click subscribe link in navigation
bar above) to receive automatic mailings of the newsletter
through email, as it is published.
The series is compiled and authored by Constantine
Kaniklidis, medical researcher, who runs the evidence-based
medicine site Evidencewatch.
Readers of this newsletter may also wish to consult
the our
Primer on Skin Anatomy and Skin
Aging, a supplement to this newsletter.
a l p h a a
n d b e t a h y d r o x y a
c i d s
alpha-hydroxy acids
Alpha-hydroxy acids (AHAs) have been
available as dermatological agents for over 20 years.
However, the use of these agents for rejuvenation dates
from ancient times (Cleopatra bathed in sour milk, which
contains the AHA lactic acid). Most alpha-hydroxy acids
are derived from foods (with those found in fruits being
called fruit acids, but technically, AHAs are are
carboxylic acids derived from fruit and milk sugars).
Malic acid comes from apples and pears, citric
acid from citrus fruits, lactic acid from milk,
tartaric acid from grapes, and glycolic acid
from sugar cane. Salicylic acid is, loosely speaking,
a beta hydroxy acid (a BHA).
Depending on the concentration, some have been
shown to be effective as peeling agents and for rejuvenation,
and all AHAs appear to act as both exfoliants and
moisturizers. Products containing AHAs vary in
concentration: consumer products usually have an AHA concentration
of 10% or less, while those used by trained cosmetologists
may be between 20% and 30%, and those used by physicians
can be 50%-70% and are classified as medications. Although
OTC (over-the-counter) commercial AHA-containing preparations
are often synthetically derived, the efficacy and operation
of synthetic AHAs is functionally equivalent to organic
source derived preparations.
AHAs contribute to a marked and visible improvement
in skin quality - both tone and texture - through their
exfoliative action, making the skin look smoother
and more youthful.. Exfoliation removes dead skin cells
from the skin's surface. Early studies demonstrated the
age-reversal activity of glycolic acid, an alpha- hydroxy
fruit acid, which sloughs off dead skin cells from the
surface of the skin in order to allow the more youthful
appearing underlying fresh cells to be visible. In effect,
topical application of these fruit AHAs significantly
reduces fine lines and wrinkles and produces a fresher
looking tone to the skin. Thus AHAs perform chemical peeling
of the human skin, a process in which the outermost layer
of dead skin cells (the stratum corneum) is removed,
exposing the fresh living cells of the underlying basal
cell layer (these two layers of cells together constitute
the skin's epidermis).
Several studies attest to the antiaging benefits of AHAs
and AHAs are not only exfoliants, but also stimulators
of collagen production and cell proliferation (growth),
with glycolic acid being significantly more effective
than malic acid.
In addition to their exfoliative action, AHAs
also have moisturizing effects: they increase the
moisture content of upper skin layers, thus smoothing
out wrinkles and fine lines and relieving dryness as well.
And AHAs also show keratolytic activity: photodamage
(sun damage) to the skin results in hyperkeratosis; hyperkeratosis
is a thickening of the skin's outer layer (the stratum
corneum) containing keratin, a tough, protective protein
(corns, calluses, and warts are all types of hyperkeratosis).
The keratolytic activity of AHAs increases turnover of
the stratum corneum, resulting in the skin appearing smoother.
other uses of AHAs
AHAs are of benefit in other skin disorders. One
such disorder is psoriasis (a skin condition of
increased epidermal production), especially when combined
with a topical steroid.
Another condition that benefits from AHAs is that of stretch
marks (technically called striae rubra and striae
alba): topical 20% glycolic acid is as effective as as
the standard treatment with tretinoin (a retinoid, discussed
in the previous issue of this newsletter), and both where
found to be safe and effective with minimal irritation.
|
|
| |
|
|
| h y d r o x y .
a c i d s |
|
|
a new
generation: polyhydroxy acids (PHAs)
Given the potential of the current generation of hydroxy
acids (alpha and beta) to increase skin sensitivity (see
above), research has focused on match or exceed the efficacy
of AHAs/BHAs yet reduce irritation that can limit the use
of traditional AHAs. Gluconolactone represents the
first of a new generation of hydroxy acids, the polyhydroxy
acids (PHAs) that is as effective as an antiaging
skin agent but less irritating than AHAs (lactobionic
acid is another PHA being researched), and gluconolactone
is now commercially available in OTC skin products.
PHAs are better tolerated than AHAs, with stinging, burning
and degree of sensitivity occurring significantly less than
with AHA treatment, the antiaging benefits being otherwise
roughly comparable. Furthermore, PHA-containing products
were compatible with African American, Caucasian, and Hispanic/Asian
skin, providing significant improvements in photoaging in
all these populations.
some cautions
Be aware, however, that using exfoliants like
the AHAs makes the skin more photosensitive, that is,
sensitive to sunlight, and that such effects can persist
up to a week after the products have been stopped. The
FDA's Center for Food Safety and Applied Nutrition (CFSAN)
determined that a month of AHA use increased sensitivity
to skin reddening by UV exposure (sunlight) by 18% (this
photosensitivity is reversed within a week of terminating
treatment). Therefore it is imperative to use a suitable
sunscreen daily to protect the newly sensitized skin.
Officially, the FDA position is: "Glycolic
and Lactic Acid, their common salts and their simple esters,
are safe for use in cosmetic products at concentrations
<10%, at final formulation pH >3.5, when formulated
to avoid increasing sun sensitivity or when directions
for use include the daily use of sun protection."
consumer guide to the safe use of AHAs/BHAs/PHAs:
1. Concentration:
Select a product with an AHA concentration of 10 percent
or less.
2. pH Range:
Select a product with a pH of 3.5 or greater (remember:
lower pH indicates greater acidity).
Note: the natural pH of the skin is in the range of 4.2
- 5.7, so this physiologic pH is altered by AHA application.
3. Photoprotection:
Select a product with an added sunscreen, or one that
has clear consumer advice to use an effective sunscreen.
4. Initial Skin Test:
Always first apply a small amount of an hydroxy acid containing
preparation to a small area of skin, and monitor for a
few days for any adverse sensitivity reaction; it is best
even during this initial trial to either use a preparation
that includes an effective sunscreen, or apply a sunscreen
before any significant exposure of that area to sunlight.
Discontinue use of a preparation if any significant sensitivity
reaction occurs, and wait at least a week to 10 days before
retrial of another preparation, after the skin has returned
to normal.
5. Product Switching:
Response and reaction to hydroxy acid containing preparations
may be fairly individual, and specific to the formulation
of the product chosen, so it may be worth trying to switch
to another preparation if any adverse reaction is encountered.
6. Building Tolerance:
It may be prudent to start with a low AHA concentration
product and one with a relatively high pH (3.5 and above,
higher is better, to a limit of about 5.7), in order to
minimize the risk of sensitivity (always use a sunscreen
with any such product if a sunscreen is not already included);
then it may be possible after a week to 10 days, to switch
to a more potent preparation (higher AHA concentration)
after developing some tolerance to the initial milder
preparation. This may be preferable to starting with a
more potent preparation.
consumer summary - the bottom
line:
Hydroxy acids demonstrate exfoliative, moisturizing,
and keratolytic activity which together result
in significant antiaging benefits to the skin, mproving
skin quality as to tone and texture, and making the skin
look smoother and more youthful, significantly reducing
wrinkles and fine lines, as well as relieving skin dryness.
If one follows our guidelines for use above, hydroxy acid
containing preparations can be both safe and effective
as antiaging agents.
how to recognize an AHA, BHA or PHA ingredient:
alpha-hydroxy
acids (AHAs)
alpha hydroxy and botanical complex
alpha-hydroxycaprylic acid
alpha-hydroxyethanoic acid + ammonium alpha-hydroxyethanoate
alpha-hydroxyoctanoic acid
citric acid
glycolic acid
glycolic acid + ammonium glycolate
glycomer in crosslinked fatty acids alpha nutrium
hydroxycaprylic acid
L-alpha hydroxy acid
lactic acid
malic acid
mixed fruit acid
sugar cane extract
triple fruit acid
tri-alpha hydroxy fruit acids
beta-hydroxy acids
(BHAs)
beta hydroxybutanoic acid
salicylic acid
tropic acid
trethocanic acid
polyhydroxy acids (PHAs)
gluconolactone
lactobionic acid
|
|
| |
|
|