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Formulations 101: Exploring the science behind cosmetic products


Dapsone has been an important antibiotic in dermatology, especially historically, in the treatment of leprosy. It has been used for both antimicrobial and anti-inflammatory purposes orally, but no topical preparation was ever available. This is because dapsone is neither water- nor oil-soluble, presenting a formulation challenge.

Q Why did it take 50 years to make a topical dapsone formulation?

Topical preparations require dissolving the active ingredient in a vehicle and placing it in an appropriate skin delivery system. This was the same challenge faced by topical metronidazole.

After much trial and error, it was found that dapsone was soluble in diethylene glycol monoethyl ether (DGME), a solvent known in the skincare industry as Transcutol (Gattefossé). The DGME provided an added benefit to the dapsone, because it also possesses anti-inflammatory qualities.

Dapsone is purchased as a white powder that must be solubulized by DGME and then added to water-soluble gel. This breakthrough allowed development of a topical dapsone gel.

Q How do the new lash-curling mascaras work? Are they safe?

A Introduced three years ago through the use of the drying properties of polymers, curling mascaras are safe. As the upper eyelid skin becomes redundant, the eyelashes appear shorter. One way to increase the apparent visible length of the eyelashes is to bend them so they project up, instead of out. This can be done with an eyelash curler, but eyelash breakage is a problem.

The need for better eyelash curl was met by the ingenuity of the cosmetic chemist. As the vehicle evaporates and polymers dry to a thin film, they shrink. If this thin film is applied to a flexible hair, the lashes will bend.

Thus, lash-curling mascaras contain a polymer that shrinks and curls the lashes. The film remains in place until removed by water or broken by further manipulation of the hair. The polymers that are used in lash-curling mascaras are the same polymers used in hair spray.

Lash-curling mascaras are safe for use in persons with sensitive skin and those who wear contact lenses. They are an easy, effective way to instantly achieve longer-appearing eyelashes.

Q How do conditioners that "strengthen" hair work?

A Hair conditioners are applied in the bath or shower after shampooing to improve the cosmetic value of the hair. The conditioner is left in contact with the hair shafts briefly and then water-rinsed.

In many ways, they can be thought of as fabric finishing for the hair. Hair can be viewed as a textile, much like wool and other natural fibers, since many of the innovations in haircare come from the fabric industry.

The longer the hair shafts grow, the more progressively damaged they become. This damage comes from combing, brushing, styling, tangling, shampooing, blow drying, curling, straightening and dyeing.

Virtually every part of haircare damages the hair shafts. This damage is more pronounced at the hair tip than at the root.

In the haircare industry, this damage is known as weathering. As the hair weathers, it loses protein. For example, the amount of methionine present in the hair shaft decreases by about 50 percent from the root to the tip. Other amino acids are lost as well.

The weakening of the hair shaft is directly proportional to the amount of protein that has been damaged. One method of temporarily restoring hair strength is to increase the protein content of the hair. Since the hair is nonliving, it is not possible to alter its composition through oral means. However, protein-containing conditioners can minimally strengthen the hair.

Weathered hair has decreased cuticular scale, allowing access to the structurally weak cortex. Hair that has been permanently dyed, bleached, chemically straightened or waved also has holes in the cuticle that were created to allow structural changes within the hair shaft to effect the cosmetic change. These holes are permanent. Protein-containing conditioners can enter the hair shaft and increase the strength of the hair by 5 to 10 percent. Only hydrolyzed protein, peptides and amino acids can diffuse into the hair shaft due to size.

However, the proteins remain in the hair shaft only until the next shampooing, when they diffuse out again with water contact. Thus, protein-containing hair conditioners must be reapplied with each shampoo. Hair conditioners can strengthen hair, but only to a small degree.

Zoe Diana Draelos, M.D., is a Dermatology Times editorial adviser and investigator, Dermatology Consulting Services, High Point, N.C. Questions may be submitted via e-mail to zdraelos@northstate.net

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