Neutralization, AHAs

Other complications caused by AHAs are extremely rare with EPS. Infection or pigmentation problems are often caused by errors made when neutralizing AHA peels. EPS is automatically neutralized by the skin s buffer capacity, and post-peel complications are far rarer than with conventional AHA peels. 

In partially neutralized AHA solutions, the acid and a lesser amount of base are combined in a reversible chemical reaction that yields unneutralized acid and a salt. 

AH2 heat of neutralization of LAS A//3 heat of dilution of 100% H2S04 to infinite dilution AHa heat of neutralization of H2S04 AHs heat of dilution of 50% NaOH to infinite dilution... 

Here we confine ourselves to some observations of the sorption of organic bases to NOM. Consider the pH-dependence (Fig. 9.18) of the sorption of quinoline (subscript q, for structure, see margin) to Aldrich humic acid (AHA). In this case, the Z)qDoc value shows a maximum at about pH 5. This corresponds to the pKia of the compound. At high pHs (i.e., pH > 7) when virtually all of the quinoline is in its nonionic form, the overall sorption is primarily determined by partitioning of this neutral species (Q) to AHA ... 

Solution Part of the pyridine has been neutralized, so there is a mixture of pyridine and pyridinium ion—Aha A buffer The fraction of pyridine that has been titrated is 4.63/19.60 = 0.236, because it takes 19.60 mL to titrate the whole sample. The fraction of pyridine remaining is 1 — 0.236 = 0.764. The pH is... 

Most neutral acids are much weaker acids in aprotic solvents than in water. This is due largely to their smaller dielectric constants, which increases the energy required for charge separation in the dissociation process. Table 7.9 summarizes the pATa values for several acids in five different solvents.62 There is a tendency in solvents with low dielectric constants, which cannot stabilize the anion of weak Brpnsted acids (HA) by hydrogen bonding, for the anion (A-) to hydrogen bond with the undissociated acid to yield the species AHA-... 

Mixture of AHAs Dermal and epidermal stimulation Easy Phytic pH 0.5, but slow-release effect -1- self-neutralizing... 

AHAs may also limit or prevent the cross-linking of proteins in the extracellular matrix. Unlike TCA or phenol, AHAs do not bind with proteins and so are not neutralized by them. The type of action they produce depends on their concentration, the pH of the solution, the pK of the acids and the contact time with the skin before neutralization with a base solution. For example, a 70% glycolic acid solution (pH 0.5 for pK 3.83) in contact with the skin for 5 minutes will be more aggressive than a partially buffered (pH 3.5) 50% solution left in contact with the skin for 2 minutes before neutralization with a base solution (a saturated solution of sodium bicarbonate, for example). 

The histological effects of AHAs also reach the dermis. Moy showed that fibroblast cultures in a glycolic environment produced up to 10 times as much hydroxyproKne (a precursor of collagen) than when cultivated in a normal saline environment. A practical problem is that AHAs do not normally reach the dermis (because, apart from Easy Phytic solution, they are neutralized before they can penetrate that far) and therefore cannot directly stimulate fibroblasts as well as they did in this in vitro study. 

This reaction is slow and reversible. The ester does not produce a peel. An alcoholic solution of AHAs would partially consist of ineffective esters that could be converted back into acid by shifting the balance of the reaction, after the acids in the solution have been medically or naturally neutralized. Applying alcohol to the skin, as a pre-peel disinfectant, does not interfere with the peel if the alcohol is given time to evaporate. 

Long-term preparation starts 4—6 weeks before a water-based AHA peel, ft can be non-specific or specific, ft is not essential, but noticeably improves results by ensuring deeper and more even penetration of the glycolic acid peel. Greater vigilance is required when applying the peel, however, as it must be neutralized more quickly. 

The contact time is the time during which the AHA is left to act before being neutralized and stopping its effect. It depends more on the appearance of erythema than on the... 

The problem with AHA peels clearly lies in the neutralization. Easy Phytic provides a solution to this difficult problem, as, in spite of its pH of 0.5, this peel does not need to be neutralized and therefore benefits from the effectiveness of 100% of the molecules applied to the skin. 

AHAs are the only peels where neutralization is important - TCA, resorcinol, salicylic acid and phenol do not need neutralizing. 

Post-inflammatory hyperpigmentation (PIH) is rare after an AHA peel. It may result from an error in assessment, indication or monitoring, but sometimes it can occur suddenly when a peel has been performed and neutralized correctly. PIH can be treated for more details, see Chapter 37. 

Alpha-hydroxy acids a new slow-release AHA complex with no neutralization required... 

The problems raised by neutralization are well known, and various solutions have been put forward to minimize the danger and risk involved with neutralizing conventional AHAs too late. Partially neutralized, less aggressive AHAs with a pH of between 3.5 and 5 can be found on the market. These acid solutions do not need neutralizing, but they do need diluting with water before any frosting occurs. Less risk, however welcome, goes hand in hand with a less effective peel. 

Ideally, the botulinum toxin should be injected a few days before the first EPS session. In this way, the two products can work together to good effect (Figure 11.4). If preferred, the botulinum toxin can of course be used after the EPS. If the botulinum toxin is injected immediately after the EPS, the needle will have to go through the non-neutralized acid solution on the skin and will take a few acid molecules into the dermis, which will make the injection more painful. It is not known how botulinum toxin and the AHAs in EPS interact in the body. The injection could be given, say, a... 

EPS is the first slow-release AHA peel not to need neutralizing, in spite of its pH of 0.5-1. This makes it extremely safe to use. It combines the known superficial peeling... 

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