Zinc Pyrithione: The Stuff Shampoos are Made of

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Zinc Pyrithione

Zinc pyrithione (abbreviated as ZnP and also known as pyrithione zinc) is an antifungal agent popularly known for and used for shampoos treating dandruff and seborrheic dermatitis or excessive inflammation of the skin due to abnormal discharge of sebum or oil.

The chemical has anti-bacterial properties and is deemed effective against many pathogens from the streptococcus and staphylococcus classes.

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Its other medical uses include treatment of psoriasis–(a condition characterized by reddish skin that may worsen into lesions and silvery-white scales and frequently causes itching and severe pain)–eczema, ringworm, fungus, athletes foot, dry skin, atypical dermatitis, tinea, vitiligo, etc.

Because of its low solubility in water at 8 ppm at neutral pH, zinc pyrithione is commonly used in outdoor paints and other products that need protection from mildew and algae.

While it is an effective algaecide ZnP is also an excellent chelating agent and thus cannot be used in paints relying on metal carboxalate catalysts to cure.

When used in latex paints and the water has a high amount of iron, a sequestering agent to bind the iron ions is needed. 

When exposed to ultraviolet light, ZnP’s decomposition is slow and gradual, providing years of protection even in direct sunlight.

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Zinc Pyrithione Compotition

The chemical’s anti-fungal effect lies mainly in its inhibition of membrane transport.

This is evidenced through the intracellular inhibition of the proton pump energizing the transport mechanism by an un-ionized pyrithione molecule. Fungi are capable of inactivating pyrithione in low concentrations.

Known under trade name zinc OMADINE, ZnP was first synthesized in 1930s. Its chemical name is zinc 2-pyridinethiol-n-oxide or also bis(1-hydroxy-2(1H)-pyridineselonato-O,S) zinc.

The summary formula is C10H8N2O2S2Zn (two organic molecules forming a complex with their oxygen and sulfur atoms around the zinc atom).

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Product list

Some of the shampoos using zinc pyrithione is Head and Shoulders, a famous brand produced by Procter & Gamble.
Procter & Gamble researchers first decided on making a new anti-dandruff shampoo in 1950 following public demand for a shampoo to help their scalp problems.

It took them nearly a decade of research to come out with a new formula which introduced the product zinc pyrithione into a shampoo for the first time.

There are now in excess of 10 different kinds of shampoo for different hair types under the Head & Shoulders banner, most if not all using the compound.

Also new technology in the manufacture of zinc pyrithione has also been developed for commercial purposes.
Pyrithione zinc, considered a particulate, was traditionally produced in a cuboidal shape and then suspended in a shampoo base.

Pyrithione zinc is a time-tested anti-dandruff agent that has good antifungal activity against the Malassezia species—a lipophilic yeast found on skin and body surfaces of 90 percent of healthy humans and animals–and some anti-inflammatory properties.

Because of advances in technology it is now possible to shape zinc pyrithione as a thin plate 2.5 microns across.
This size is important, since the larger cuboidal pyrithione zinc was deemed too large to precipitate on the scalp during shampooing.

Moreover plate-like pyrithione zinc less than 2.5 microns is considered too small and is found to have been completely rinsed from the scalp following shampooing.

Through testing it was shown that 2.5 micron pyrithione zinc is able to precipitate from the shampoo, remaining on the scalp and thus resist water rinsing.

As a result this provides for a potent antifungal to remain on the scalp to prevent re-colonization or revival of the Malassezia species and slow down the return of dandruff and resultant seborrheic dermatitis.

Due to these findings, many new dandruff shampoos use the compound and lay claim that they improve hair appearance while delaying the return of scalp itching and flaking.

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