Free
Acid Definition/What does pH got to do with it??
The
acid in
AHA preparations may be free (popularly called "unbuffered" or "not
neutralized") or it may be partially neutralized or buffered (partially
neutralized means that the pH is adjusted to make the solution less
acidic).
In
a glycolic acid solution, AHAs are present partly as free acid (neutral molecules that
penetrate skin) and partly
dissociated as the anion (charged molecules that do not penetrate skin). The proportions
of free acid and anion are determined by pH (Johnson et al., 1997).
So, is pH important to effectiveness of the Peel??
Yes, it most definitely is!
The objective
of neutralization is to raise the pH of an acid from below 2 to a value of 2.5 to 3.5, to provide
a
safe,
effective product that will accommodate the skin's natural pH of 4.2 to 5.6.
In partially neutralized AHA solutions, the acid and a lesser amount of base
are
combined in a reversible chemical reaction that yields un-neutralized ("free") acid and a
salt.
The resulting
solution has less free acid and a higher pH than a solution that has not been neutralized.
In partially neutralized formulations, the salt functions as a reservoir of
acid that is
available for second-phase penetration.
In
other words, when a glycolic acid solution has had the pH adjusted,
anywhere in the neighborhood of 2.5 for times peels, to 3.5 for
leave-on products, some of the free acid has been converted to a
"salt". The solution is part acid, and part acid salt, rather than all
acid.
The
pH adjusted, partially neutralized acid solution is NOT LESS EFFECTIVE
at all! It is actually more effective, and safer to use. The acid
still does it's job, but the action of the acid has been adjusted to be
rather like a "time-released" formula, rather than a rapid burning of
the skin. This is much better and more effective for the skin.
This means that partially neutralized formulas
(pH adjusted) can deliver as much, if not more, alpha-hydroxy acid than free acid formulas, but in a
safer, "time-released" manner.
AHA
preparations designed for home use generally are neutralized or buffered to a
pH of
2.5 to 4.5. - That is, the most effective formulations! The lower pH
formulations deliver the acid faster, almost like "all at once" and
then the action stops. The formulation with properly adjusted pH
deliver the acid gradually into the skin, can stay longer on the skin,
and are thus more effective in terms of delivery and results!
Peeling
solutions with a pH below 2 have the potential to induce crusting and serious skin damage, which is
not seen with the partially neutralized solutions. There is no evidence that creating skin damage or swelling leads to a more favorable result of the peel.
Therefore, the use of
partially neutralized glycolic
acid solutions seems prudent, since they have a better
safety profile than low-pH solutions containing only free glycolic acid (Becker et al., 1996).
In clinical
and in vitro studies, partially neutralized glycolic acid and other AHA
preparations
were beneficial to the skin, in terms of rejuvenation or remodeling of tissue.
Clinical
studies have shown that a partially neutralized lactic acid preparation
improves the skin,
both in appearance and histologically.
Other studies using skin tissue cultures showed that
partially neutralized glycolic
acid stimulates fibroblast proliferation -- an index of
tissue regeneration (Rubin, 1996).
Looking at electrical conductance of the
skin (an
indicator of water content or moisturization), higher pH products (those that
have been
partially neutralized) are better moisturizers than lower pH preparations
(Rubin, 1996).
So,
in conclusion, the safest and most effective method of skin peeling at
home involves using an acid product that has been partially
neutralized, with the pH adjusted to 2.5 for a timed peel, and to 3.5
for a leave on treatment.
