Zinc oxide

Zinc is a trace element, and it is not synthesized by the human body. The element was identified in the 1960s as being essential for human health and development. Zinc is a cofactor in more than 300 enzymes necessary for cell function. In the dermatologic realm, zinc deficiency has been associated with skin alterations, delayed wound healing, and hair loss.

Zinc oxide (ZnO) is a metal oxide that also has a broad profile in dermatology. It is perhaps best known as a physical sunscreen ingredient. ZnO and titanium dioxide (TiO₂) have long been used in this manner. Both ZnO and TiO₂ also have been increasingly used to replace large-particle compounds in numerous cosmetics and sunscreens. These two compounds have demonstrated effective protection against UV-induced damage, providing stronger protection against UV radiation while leaving less white residue than previous generations of physical sunscreens.

Particles of ZnO in earlier sunscreens were found to be too large to penetrate the stratum corneum and, thus, were deemed biologically inactive (J. Am. Acad. Dermatol. 1999;40:85-90). However, in novel nanoparticle form, such metal oxides absorb UV radiation, leading to photocatalysis and the release of reactive oxygen species (Australas. J. Dermatol. 2011;52:1-6). Indeed, nanoparticles exhibit new physiochemical properties as a result of increased surface area as compared to large-form products, and the potential adverse effects of the novel nanoparticle formulations in sunscreens cannot be adequately extrapolated from the effects of older-generation larger-particle skin care products (J. Drugs Dermatol. 2010;9:475-81; Int. J. Dermatol. 2011;50:247-54. The relative safety of ZnO nanoparticles will be discussed in a future column. The focus in this column will be a brief comparison with TiO₂ and other indications for ZnO.

ZnO and TiO₂

While numerous studies explore both TiO₂ and ZnO, the latter is noted for greater versatility within the dermatologic armamentarium. In addition, ZnO is less photoactive and is associated with a lower refractive index in visible light than TiO₂ (1.9 vs. 2.6, respectively) (J. Am. Acad. Dermatol. 1999;40:85-90); therefore, TiO₂ appears whiter and is more difficult to incorporate into transparent products.

Another important difference is the spectrum of action. That is, only avobenzone (butyl methoxydibenzoylmethane) and ZnO are approved in the United States for broad-spectrum protection against UVA wavelengths greater than 360 nm, because TiO₂ has been shown to be effective only against UV wavelengths less than 360 nm (UVA is 320-400 nm). In a study by Beasley and Meyer, TiO₂ delivered neither the same level of UVA attenuation nor protection from UVA to human skin as did photostabilized formulations of avobenzone or ZnO. Therefore, TiO₂ is not a suitable substitute for avobenzone and ZnO for strong UVA protection (Am. J. Clin. Dermatol. 2010;11:413-21).

Indications beyond photoprotection

More than 20 years ago, Hughes and McLean showed that a ZnO tape was effective in dressing fingertip and soft tissue injuries that were resistant to healing (Arch. Emerg. Med. 1988;5:223-7). More recently, Parboteeah and Brown demonstrated the efficacy of treating recalcitrant venous leg ulcers with ZnO paste bandages (Br. J. Nurs. 2008;17:S30, S32, S34-6). In addition, Treadwell has shown that the weekly application of ZnO compression dressings to surgical wounds of the lower leg promotes healing (Dermatol. Surg. 2011;37:166-7).

Micronized zinc oxide is included in a 4% hydroquinone/10% L-ascorbic acid treatment system recently found (in a small study of 34 females) to be effective in alleviating early signs of photodamage in normal to oily skin. Thirty patients, with minimal or mild facial photodamage and hyperpigmentation, completed the 12-week treatment regimen. All the participants were satisfied with the appearance of their skin after the study, with median scores for all assessment parameters significantly improved compared with baseline (J. Drugs Dermatol. 2011;10:1455-61). ZnO also is an active ingredient in formulations intended to support the healing of perianal eczema (Hautarzt. 2010;61:33-8).

A 2001 report on a series of blinded, randomized clinical trials conducted by Baldwin et al. showed that clinical benefits were derived from the continuous topical administration of a ZnO/petrolatum formulation in a diaper introduced at that time. The first study was undertaken to verify that the ZnO/petrolatum formulation was indeed transferred from the diaper to the child’s skin. Stratum corneum (SC) samples were analyzed from each child after the wearing of a single diaper for 3 hours or multiple diapers for 24 hours. The results indicated effective transfer, with ZnO increasing in the SC from 4.2 mcg/cm² at 3 hours to more than 8 mcg/cm² at 24 hours.

The second study of the formulation, in an adult arm model, assessed the prevention of irritation and SC damage induced by sodium laureth sulfate. The investigators found that the ZnO/petrolatum combination yielded significant reductions in SC damage and erythema. The third study, a 4-week trial in which 268 infants were assessed, considered the effects of the formulation on erythema and diaper rash. Half of the infants wore the test diaper and half used a control diaper lacking the ZnO/petrolatum product. Significant reductions in erythema and diaper rash were indeed observed in the test group (J. Eur. Acad. Dermatol. Venereol. 2001;15 Suppl 1:5-11).

A 2009 study showed that an unmedicated ZnO/petrolatum paste was effective in restoring the properties of the skin, allowing for balanced transepidermal water loss and water retention by SC previously compromised by diaper dermatitis. This skin condition affects approximately 50% of infants and a small percentage of the bedridden elderly (Int. J. Cosmet. Sci. 2009;31:369-74).

In 2010, a study that assessed the effectiveness of topical ZnO ointment using the rabbit ear hypertrophic scar model showed that the application of 40% ZnO significantly reduced clinical scar hypertrophy scores at 6 weeks compared with placebo. The researchers concluded that these results may suggest clinical applications for ZnO in the treatment of hypertrophic scars in humans (Burns 2010;36:1027-35). In addition, ZnO has demonstrated antibacterial properties, with nanoparticles exhibiting more potent antibacterial activity than bulk ZnO (Sci. Technol. Adv. Mater. 2008;9:1-7).

Products

ZnO is a key ingredient in calamine lotion, an antipruritic compound used to treat various mild conditions such as bites and stings from insects, eczema, poison ivy, rashes, and sunburn. It is also available over the counter in ointment or suppository form for healing hemorrhoids and fissures. In addition, ZnO is used widely in baby powders, barrier creams, moisturizers, antiseptic ointments, antidandruff shampoos, athletic bandage tape, and, of course, sunscreens.

Conclusion

ZnO is a versatile inorganic metal oxide with multiple indications in dermatology. Consequently, it is included in a wide array of skin care products, including shampoos, moisturizers, and sunscreens. Its use in nanoparticle form, along with the similar use of its physical sunscreen counterpart TiO₂, represents one of the many subjects debated within the larger context of sunscreen use. The next edition of this column will focus on the relative safety of zinc oxide nanoparticles.

Dr. Baumann is chief executive officer of the Baumann Cosmetic & Research Institute in Miami Beach. She founded the cosmetic dermatology center at the University of Miami in 1997. Dr. Baumann wrote the textbook "Cosmetic Dermatology: Principles and Practice" (McGraw-Hill, April 2002), and a book for consumers, "The Skin Type Solution" (Bantam, 2006). She has contributed to the Cosmeceutical Critique column in Skin & Allergy News since January 2001 and joined the editorial advisory board in 2004. Dr. Baumann has received funding for clinical grants from Allergan, Aveeno, Avon Products, Galderma, Mary Kay, Medicis Pharmaceuticals, Neutrogena, Philosophy, Stiefel, Topix Pharmaceuticals, and Unilever.

This column, "Cosmeceutical Critique," appears regularly in Skin & Allergy News, a publication of Frontline Medical News.

Zinc is a trace element, and it is not synthesized by the human body. The element was identified in the 1960s as being essential for human health and development. Zinc is a cofactor in more than 300 enzymes necessary for cell function. In the dermatologic realm, zinc deficiency has been associated with skin alterations, delayed wound healing, and hair loss.

Zinc oxide (ZnO) is a metal oxide that also has a broad profile in dermatology. It is perhaps best known as a physical sunscreen ingredient. ZnO and titanium dioxide (TiO₂) have long been used in this manner. Both ZnO and TiO₂ also have been increasingly used to replace large-particle compounds in numerous cosmetics and sunscreens. These two compounds have demonstrated effective protection against UV-induced damage, providing stronger protection against UV radiation while leaving less white residue than previous generations of physical sunscreens.

Particles of ZnO in earlier sunscreens were found to be too large to penetrate the stratum corneum and, thus, were deemed biologically inactive (J. Am. Acad. Dermatol. 1999;40:85-90). However, in novel nanoparticle form, such metal oxides absorb UV radiation, leading to photocatalysis and the release of reactive oxygen species (Australas. J. Dermatol. 2011;52:1-6). Indeed, nanoparticles exhibit new physiochemical properties as a result of increased surface area as compared to large-form products, and the potential adverse effects of the novel nanoparticle formulations in sunscreens cannot be adequately extrapolated from the effects of older-generation larger-particle skin care products (J. Drugs Dermatol. 2010;9:475-81; Int. J. Dermatol. 2011;50:247-54. The relative safety of ZnO nanoparticles will be discussed in a future column. The focus in this column will be a brief comparison with TiO₂ and other indications for ZnO.

ZnO and TiO₂

While numerous studies explore both TiO₂ and ZnO, the latter is noted for greater versatility within the dermatologic armamentarium. In addition, ZnO is less photoactive and is associated with a lower refractive index in visible light than TiO₂ (1.9 vs. 2.6, respectively) (J. Am. Acad. Dermatol. 1999;40:85-90); therefore, TiO₂ appears whiter and is more difficult to incorporate into transparent products.

Another important difference is the spectrum of action. That is, only avobenzone (butyl methoxydibenzoylmethane) and ZnO are approved in the United States for broad-spectrum protection against UVA wavelengths greater than 360 nm, because TiO₂ has been shown to be effective only against UV wavelengths less than 360 nm (UVA is 320-400 nm). In a study by Beasley and Meyer, TiO₂ delivered neither the same level of UVA attenuation nor protection from UVA to human skin as did photostabilized formulations of avobenzone or ZnO. Therefore, TiO₂ is not a suitable substitute for avobenzone and ZnO for strong UVA protection (Am. J. Clin. Dermatol. 2010;11:413-21).

Indications beyond photoprotection

More than 20 years ago, Hughes and McLean showed that a ZnO tape was effective in dressing fingertip and soft tissue injuries that were resistant to healing (Arch. Emerg. Med. 1988;5:223-7). More recently, Parboteeah and Brown demonstrated the efficacy of treating recalcitrant venous leg ulcers with ZnO paste bandages (Br. J. Nurs. 2008;17:S30, S32, S34-6). In addition, Treadwell has shown that the weekly application of ZnO compression dressings to surgical wounds of the lower leg promotes healing (Dermatol. Surg. 2011;37:166-7).

Micronized zinc oxide is included in a 4% hydroquinone/10% L-ascorbic acid treatment system recently found (in a small study of 34 females) to be effective in alleviating early signs of photodamage in normal to oily skin. Thirty patients, with minimal or mild facial photodamage and hyperpigmentation, completed the 12-week treatment regimen. All the participants were satisfied with the appearance of their skin after the study, with median scores for all assessment parameters significantly improved compared with baseline (J. Drugs Dermatol. 2011;10:1455-61). ZnO also is an active ingredient in formulations intended to support the healing of perianal eczema (Hautarzt. 2010;61:33-8).

A 2001 report on a series of blinded, randomized clinical trials conducted by Baldwin et al. showed that clinical benefits were derived from the continuous topical administration of a ZnO/petrolatum formulation in a diaper introduced at that time. The first study was undertaken to verify that the ZnO/petrolatum formulation was indeed transferred from the diaper to the child’s skin. Stratum corneum (SC) samples were analyzed from each child after the wearing of a single diaper for 3 hours or multiple diapers for 24 hours. The results indicated effective transfer, with ZnO increasing in the SC from 4.2 mcg/cm² at 3 hours to more than 8 mcg/cm² at 24 hours.

The second study of the formulation, in an adult arm model, assessed the prevention of irritation and SC damage induced by sodium laureth sulfate. The investigators found that the ZnO/petrolatum combination yielded significant reductions in SC damage and erythema. The third study, a 4-week trial in which 268 infants were assessed, considered the effects of the formulation on erythema and diaper rash. Half of the infants wore the test diaper and half used a control diaper lacking the ZnO/petrolatum product. Significant reductions in erythema and diaper rash were indeed observed in the test group (J. Eur. Acad. Dermatol. Venereol. 2001;15 Suppl 1:5-11).

A 2009 study showed that an unmedicated ZnO/petrolatum paste was effective in restoring the properties of the skin, allowing for balanced transepidermal water loss and water retention by SC previously compromised by diaper dermatitis. This skin condition affects approximately 50% of infants and a small percentage of the bedridden elderly (Int. J. Cosmet. Sci. 2009;31:369-74).

In 2010, a study that assessed the effectiveness of topical ZnO ointment using the rabbit ear hypertrophic scar model showed that the application of 40% ZnO significantly reduced clinical scar hypertrophy scores at 6 weeks compared with placebo. The researchers concluded that these results may suggest clinical applications for ZnO in the treatment of hypertrophic scars in humans (Burns 2010;36:1027-35). In addition, ZnO has demonstrated antibacterial properties, with nanoparticles exhibiting more potent antibacterial activity than bulk ZnO (Sci. Technol. Adv. Mater. 2008;9:1-7).

Products

ZnO is a key ingredient in calamine lotion, an antipruritic compound used to treat various mild conditions such as bites and stings from insects, eczema, poison ivy, rashes, and sunburn. It is also available over the counter in ointment or suppository form for healing hemorrhoids and fissures. In addition, ZnO is used widely in baby powders, barrier creams, moisturizers, antiseptic ointments, antidandruff shampoos, athletic bandage tape, and, of course, sunscreens.

Conclusion

ZnO is a versatile inorganic metal oxide with multiple indications in dermatology. Consequently, it is included in a wide array of skin care products, including shampoos, moisturizers, and sunscreens. Its use in nanoparticle form, along with the similar use of its physical sunscreen counterpart TiO₂, represents one of the many subjects debated within the larger context of sunscreen use. The next edition of this column will focus on the relative safety of zinc oxide nanoparticles.

Dr. Baumann is chief executive officer of the Baumann Cosmetic & Research Institute in Miami Beach. She founded the cosmetic dermatology center at the University of Miami in 1997. Dr. Baumann wrote the textbook "Cosmetic Dermatology: Principles and Practice" (McGraw-Hill, April 2002), and a book for consumers, "The Skin Type Solution" (Bantam, 2006). She has contributed to the Cosmeceutical Critique column in Skin & Allergy News since January 2001 and joined the editorial advisory board in 2004. Dr. Baumann has received funding for clinical grants from Allergan, Aveeno, Avon Products, Galderma, Mary Kay, Medicis Pharmaceuticals, Neutrogena, Philosophy, Stiefel, Topix Pharmaceuticals, and Unilever.

This column, "Cosmeceutical Critique," appears regularly in Skin & Allergy News, a publication of Frontline Medical News.

Zinc is a trace element, and it is not synthesized by the human body. The element was identified in the 1960s as being essential for human health and development. Zinc is a cofactor in more than 300 enzymes necessary for cell function. In the dermatologic realm, zinc deficiency has been associated with skin alterations, delayed wound healing, and hair loss.

Zinc oxide (ZnO) is a metal oxide that also has a broad profile in dermatology. It is perhaps best known as a physical sunscreen ingredient. ZnO and titanium dioxide (TiO₂) have long been used in this manner. Both ZnO and TiO₂ also have been increasingly used to replace large-particle compounds in numerous cosmetics and sunscreens. These two compounds have demonstrated effective protection against UV-induced damage, providing stronger protection against UV radiation while leaving less white residue than previous generations of physical sunscreens.

Particles of ZnO in earlier sunscreens were found to be too large to penetrate the stratum corneum and, thus, were deemed biologically inactive (J. Am. Acad. Dermatol. 1999;40:85-90). However, in novel nanoparticle form, such metal oxides absorb UV radiation, leading to photocatalysis and the release of reactive oxygen species (Australas. J. Dermatol. 2011;52:1-6). Indeed, nanoparticles exhibit new physiochemical properties as a result of increased surface area as compared to large-form products, and the potential adverse effects of the novel nanoparticle formulations in sunscreens cannot be adequately extrapolated from the effects of older-generation larger-particle skin care products (J. Drugs Dermatol. 2010;9:475-81; Int. J. Dermatol. 2011;50:247-54. The relative safety of ZnO nanoparticles will be discussed in a future column. The focus in this column will be a brief comparison with TiO₂ and other indications for ZnO.

ZnO and TiO₂

While numerous studies explore both TiO₂ and ZnO, the latter is noted for greater versatility within the dermatologic armamentarium. In addition, ZnO is less photoactive and is associated with a lower refractive index in visible light than TiO₂ (1.9 vs. 2.6, respectively) (J. Am. Acad. Dermatol. 1999;40:85-90); therefore, TiO₂ appears whiter and is more difficult to incorporate into transparent products.

Another important difference is the spectrum of action. That is, only avobenzone (butyl methoxydibenzoylmethane) and ZnO are approved in the United States for broad-spectrum protection against UVA wavelengths greater than 360 nm, because TiO₂ has been shown to be effective only against UV wavelengths less than 360 nm (UVA is 320-400 nm). In a study by Beasley and Meyer, TiO₂ delivered neither the same level of UVA attenuation nor protection from UVA to human skin as did photostabilized formulations of avobenzone or ZnO. Therefore, TiO₂ is not a suitable substitute for avobenzone and ZnO for strong UVA protection (Am. J. Clin. Dermatol. 2010;11:413-21).

Indications beyond photoprotection

More than 20 years ago, Hughes and McLean showed that a ZnO tape was effective in dressing fingertip and soft tissue injuries that were resistant to healing (Arch. Emerg. Med. 1988;5:223-7). More recently, Parboteeah and Brown demonstrated the efficacy of treating recalcitrant venous leg ulcers with ZnO paste bandages (Br. J. Nurs. 2008;17:S30, S32, S34-6). In addition, Treadwell has shown that the weekly application of ZnO compression dressings to surgical wounds of the lower leg promotes healing (Dermatol. Surg. 2011;37:166-7).

Micronized zinc oxide is included in a 4% hydroquinone/10% L-ascorbic acid treatment system recently found (in a small study of 34 females) to be effective in alleviating early signs of photodamage in normal to oily skin. Thirty patients, with minimal or mild facial photodamage and hyperpigmentation, completed the 12-week treatment regimen. All the participants were satisfied with the appearance of their skin after the study, with median scores for all assessment parameters significantly improved compared with baseline (J. Drugs Dermatol. 2011;10:1455-61). ZnO also is an active ingredient in formulations intended to support the healing of perianal eczema (Hautarzt. 2010;61:33-8).

A 2001 report on a series of blinded, randomized clinical trials conducted by Baldwin et al. showed that clinical benefits were derived from the continuous topical administration of a ZnO/petrolatum formulation in a diaper introduced at that time. The first study was undertaken to verify that the ZnO/petrolatum formulation was indeed transferred from the diaper to the child’s skin. Stratum corneum (SC) samples were analyzed from each child after the wearing of a single diaper for 3 hours or multiple diapers for 24 hours. The results indicated effective transfer, with ZnO increasing in the SC from 4.2 mcg/cm² at 3 hours to more than 8 mcg/cm² at 24 hours.

The second study of the formulation, in an adult arm model, assessed the prevention of irritation and SC damage induced by sodium laureth sulfate. The investigators found that the ZnO/petrolatum combination yielded significant reductions in SC damage and erythema. The third study, a 4-week trial in which 268 infants were assessed, considered the effects of the formulation on erythema and diaper rash. Half of the infants wore the test diaper and half used a control diaper lacking the ZnO/petrolatum product. Significant reductions in erythema and diaper rash were indeed observed in the test group (J. Eur. Acad. Dermatol. Venereol. 2001;15 Suppl 1:5-11).

A 2009 study showed that an unmedicated ZnO/petrolatum paste was effective in restoring the properties of the skin, allowing for balanced transepidermal water loss and water retention by SC previously compromised by diaper dermatitis. This skin condition affects approximately 50% of infants and a small percentage of the bedridden elderly (Int. J. Cosmet. Sci. 2009;31:369-74).

In 2010, a study that assessed the effectiveness of topical ZnO ointment using the rabbit ear hypertrophic scar model showed that the application of 40% ZnO significantly reduced clinical scar hypertrophy scores at 6 weeks compared with placebo. The researchers concluded that these results may suggest clinical applications for ZnO in the treatment of hypertrophic scars in humans (Burns 2010;36:1027-35). In addition, ZnO has demonstrated antibacterial properties, with nanoparticles exhibiting more potent antibacterial activity than bulk ZnO (Sci. Technol. Adv. Mater. 2008;9:1-7).

Products

ZnO is a key ingredient in calamine lotion, an antipruritic compound used to treat various mild conditions such as bites and stings from insects, eczema, poison ivy, rashes, and sunburn. It is also available over the counter in ointment or suppository form for healing hemorrhoids and fissures. In addition, ZnO is used widely in baby powders, barrier creams, moisturizers, antiseptic ointments, antidandruff shampoos, athletic bandage tape, and, of course, sunscreens.

Conclusion

ZnO is a versatile inorganic metal oxide with multiple indications in dermatology. Consequently, it is included in a wide array of skin care products, including shampoos, moisturizers, and sunscreens. Its use in nanoparticle form, along with the similar use of its physical sunscreen counterpart TiO₂, represents one of the many subjects debated within the larger context of sunscreen use. The next edition of this column will focus on the relative safety of zinc oxide nanoparticles.

Dr. Baumann is chief executive officer of the Baumann Cosmetic & Research Institute in Miami Beach. She founded the cosmetic dermatology center at the University of Miami in 1997. Dr. Baumann wrote the textbook "Cosmetic Dermatology: Principles and Practice" (McGraw-Hill, April 2002), and a book for consumers, "The Skin Type Solution" (Bantam, 2006). She has contributed to the Cosmeceutical Critique column in Skin & Allergy News since January 2001 and joined the editorial advisory board in 2004. Dr. Baumann has received funding for clinical grants from Allergan, Aveeno, Avon Products, Galderma, Mary Kay, Medicis Pharmaceuticals, Neutrogena, Philosophy, Stiefel, Topix Pharmaceuticals, and Unilever.

This column, "Cosmeceutical Critique," appears regularly in Skin & Allergy News, a publication of Frontline Medical News.