Dimethicone

Dimethicone is a very popular moisturizing ingredient because of its multifunctional properties. It works as an occlusive, reducing water loss from the skin, as an emollient, making the skin soft and smooth to the touch, and also as a barrier repair ingredient.

Effects


Grade Level of Evidence
A Multiple double-blind, controlled clinical trials.
B 1 double-blind, controlled clinical trial.
C At least 1 controlled or comparative clinical trial.
D Uncontrolled, observational, animal or in-vitro studies only.
Grade Effect Size of Effect Comments

C

Increased skin hydration

Strong

Functions as both an occlusive and as an emollient. More hydrating than petrolatum, but less so than glycerin.

C

Dermatitis treatment

Moderate

Useful in treating contact dermatitis, hand dermatitis, diaper dermatitis and incontinence-associated dermatitis.

C

Less visible scars

Moderate

Dimethicone gel sheets can be used together with topical vitamin E to treat hypertropic scars and keloids.

D

Enhanced barrier function

Mild

Has a weak effect on restoring the epidermal barrier, probably by stimulating keratinocyte proliferation.

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Scientific Research


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Table of contents:

1. Sources

Dimethicone, also known as polydimethylsiloxane (PDMS), is a fluid mixture of fully methylated linear siloxane polymers end-blocked with trimethylsiloxy units.[1] It is used extensively in cosmetic formulations as a conditioning agent,[1] skin protectant[2][3] and moisturizer. It also influences the sensory properties and hence the skin feel of cosmetic formulations.[4][5]

2. Bioavailability

Clinical and animal studies have reported that dimethicone is not absorbed following dermal exposure.[1] Dimethicone does not alter the phase-transition temperatures and enthalpies of the stratum corneum lipids[6] and therefore does not act as a penetration enhancer.[7] In fact, a barrier cream based on dimethicone has been demonstrated to protect against the penetration of S. mansoni cercariae, the parasitic worm that causes schistosomiasis, into human skin.[8]

3. Effects on the skin

3.1 Increased moisturization

Dimethicone is the second most common active agent in moisturizers, and is usually used in oil-free facial moisturizers.[9][10] It has both occlusive and emollient properties, which means that it can physically block transepidermal water loss (TEWL) in the stratum corneum[11] as well as make the skin smooth and soft to the touch by filling in the spaces between desquamating corneocytes.[9] In one study, it was found to have greater hydration potential than petrolatum, but to be less hydrating than glycerin.[12]

Because dimethicone is non-comedogenic and hypoallergenic, it is considered suitable for acne patients and patients with sensitive skin. Indeed, an analysis of 52 moisturizers for acne revealed that dimethicone, along with glycerin, were the the most common ingredients used.[10]

3.2 Improved barrier function

Dimethicone is considered a barrier repair ingredient because it helps reduce transepidermal water loss (TEWL), though it is less effective than petrolatum in this respect.[13]

Including dimethicone in topical acne medications can minimize treatment-related irritation by reducing the impairment of the epidermal barrier and restoring its function. Multiple studies have shown that topical gels containing clindamycin and benzoyl peroxide decrease side effects such as erythema, dryness, scaling, pruritus and hyperpigmentation, when formulated with dimethicone and glycerin as hydrating excipients.[14][15][16][17] In one study, the clindamycin-benzoyl peroxide gels containing dimethicone and glycerin actually produced a more consistent reduction in the total number of inflammatory lesions over 12 weeks, compared to gel without the additives.[18] Treatment satisfaction was also higher,[18] which may have contributed to the greater efficacy by encouraging patient compliance to the treatment regimen.

The presence of dimethicone in the vehicle of sunscreens may also help prevent irritation of facial skin caused by other sunscreen ingredients in patients suffering from rosacea.[19]

In a study on 15 adult women who applied a moisturizer containing 2.5% dimethicone, 10% glycerin and 30% silicone twice daily to their photoaged forearms for 28 days, transepidermal water loss was found to have decreased by 13% compared to baseline, indicative of an improved skin barrier. Histology showed that the maximal epidermal thickness had increased by 0.019 mm (32%) from baseline, and revealed that the expression of keratins 6 and 16, which are commonly associated with keratinocyte proliferation, had been induced. In addition, melanin levels were lower and melanin was noted at more superficial levels of the epidermis. Together, this suggested that epidermal proliferation had occurred and an faster transit of keratinocytes, resulting in the removal of melanin-containing cells.[20]

3.3 Dermatitis treatment

Dimethicone's skin protectant properties enables it to be used for the prevention or treatment of several types of dermatitis. An early double-blind trial carried out on 62 infants with diaper dermatitis found that a topical preparation containing dimethicone, nystatin, benzalkonium chloride and hydrocortisone was successful in curing 84% of the infants treated after 7 days, with a significant improvement in clinical signs and symptoms such as erythema, weeping, tissue maceration and irritability produced within 48 hours in most cases.[21] A recent pilot study also suggests that a topical solution containing dimethicone (LOYON) can facilitate the removal of scaling in infants and children with cradle cap, the common term for infantile or neonatal seborrheic dermatitis.[22]

Moreover, a 3-in-1 perineal care washcloth impregnated with 3% dimethicone led to a significantly reduced prevalence of incontinence-associated dermatitis (IAD) in a randomized, controlled clinical trial involving 141 nursing home residents. Only 8.1% of the residents in the experimental group were judged to still suffer from IAD after 120 days, down from 22.3% at baseline. By comparison, 27.1% of the residents in the control group had IAD at the end of the experiment, up from 22.8% at baseline. There was also a trend towards less severe IAD lesions in the experimental group, though this was not significant.[23]

Another study sought to determine if a protective foam containing dimethicone and glycerin could improve chronic hand dermatitis of an occupational nature, and found that 21 out of 30 subjects (75%) improved over the course of 6 weeks and 16 (54%) reduced their usage of corticosteroids over the same time period.[24] A dimethicone skin protectant lotion has also been shown to inhibit sodium lauryl sulphate (SLS)-induced dermatitis, indicating that it may be useful in work or home environments to prevent dermatitis triggered by exposure to skin irritants.[25]

More convincingly, a systematic review of contact dermatitis treatment and prevention has also concluded that barrier creams containing dimethicone can prevent irritant contact dermatitis.[26]

However, dimethicone-containing products appear to be less effective at protecting the skin from insults or maceration than petrolatum-containing products.[12] A skin protectant solution containing 2% dimethicone was also ineffective in improving the clinical signs and transepidermal water loss in dogs with canine atopic dermatitis.[27]

3.4 Treatment of scars and keloids

The wrapping of dimethicone plates on the surfaces of hypertrophic scars and keloids has been reported to be an effective therapeutic approach for prophylaxis through its action on fibroblasts and subcutaneous tissue, with the addition of vitamin E further increasing the extent of improvement[28]

3.5 Treatment of head lice

Numerous clinical trials have established the efficacy of dimethicone-based formulations in clearing head louse infestations.[29][30][31][32][33][34] Its mode of action is physical; it exerts its lethal effects by displacing air in the tracheal system of the head.[35] This inhibits water excretion, which causes physiological stress and eventually death either through prolonged immobilisation or the rupture of the gut.[36]

Dimethicone also exhibits efficacy in killing the eggs of head lice, an important part of head lice treatment.[37][38][39][40]

4. Safety

Dimethicone as well as many of its crosspolymers are considered to be safe as used in cosmetic formulations by the Cosmetic Ingredients Review Expert Panel.[1][41]

4.1 Adverse skin reactions

The majority of the dermal irritation studies on rabbits classified dimethicone as a minimal irritant. It was also not a sensitizer in 4 assays using mice and guinea pigs, nor was it a sensitizer at a concentration of 5% in a clinical repeated insult patch test on 83 panelists.[1]

4.2 No evidence of genotoxicity

Dimethicone was negative in all genotoxicity assays, including an oral and dermal dose carcinogenicity test on mice.[1]

Scientific References


  1. Nair B; Cosmetic Ingredients Review Expert Panel. Final report on the safety assessment of stearoxy dimethicone, dimethicone, methicone, amino bispropyl dimethicone, aminopropyl dimethicone, amodimethicone, amodimethicone hydroxystearate, behenoxy dimethicone, C24-28 alkyl methicone, C30-45 alkyl methicone, C30-45 alkyl dimethicone, cetearyl methicone, cetyl dimethicone, dimethoxysilyl ethylenediaminopropyl dimethicone, hexyl methicone, hydroxypropyldimethicone, stearamidopropyl dimethicone, stearyl dimethicone, stearyl methicone, and vinyldimethicone. Int J Toxicol. (2003)
  2. Carter BN 2nd, Sherman RT. Dimethicone (silicone) skin protection in surgical patients. AMA Arch Surg. (1957)
  3. Banerjee BN, Chakrabarty J. Dimethicone 20 B.P.C. (SILOCERM)--a new multipurpose skin protective barrier ointment as prophylaxis in skin diseases, a preliminary report. Indian J Dermatol. (1969)
  4. Lemaitre-Aghazarian V, et. al. Texture optimization of water-in-oil emulsions. Pharm Dev Technol. (2004)
  5. Parente ME, Gámbaro A, Solana G. Study of sensory properties of emollients used in cosmetics and their correlation with physicochemical properties. J Cosmet Sci. (2005)
  6. Leopold CS, Lippold BC. An attempt to clarify the mechanism of the penetration enhancing effects of lipophilic vehicles with differential scanning calorimetry (DSC). J Pharm Pharmacol. (1995)
  7. Leopold CS, Lippold BC. Enhancing effects of lipophilic vehicles on skin penetration of methyl nicotinate in vivo. J Pharm Sci. (1995)
  8. Ingram RJ, et. al. Dimethicone barrier cream prevents infection of human skin by schistosome cercariae: evidence from Franz cell studies. J Parasitol. (2002)
  9. Draelos ZD. Active agents in common skin care products. Plast Reconstr Surg. (2010)
  10. Chularojanamontri L, et. al. Moisturizers for Acne: What are their Constituents? J Clin Aesthet Dermatol. (2014)
  11. Lynde CW. Moisturizers: what they are and how they work. Skin Therapy Lett. (2001)
  12. Hoggarth A, et. al. A controlled, three-part trial to investigate the barrier function and skin hydration properties of six skin protectants. Ostomy Wound Manage. (2005)
  13. Draelos ZD. New treatments for restoring impaired epidermal barrier permeability: skin barrier repair creams. Clin Dermatol. (2012)
  14. Del Rosso JQ. The role of the vehicle in combination acne therapy. Cutis. (2005)
  15. Taylor SC. Utilizing combination therapy for ethnic skin. Cutis. (2007)
  16. Del Rosso JQ. Combination topical therapy in the treatment of acne. Cutis. (2006)
  17. Draelos ZD, et. al. The effect of vehicle formulation on acne medication tolerability. Cutis. (2008)
  18. Dhawan SS. Comparison of 2 clindamycin 1%-benzoyl peroxide 5% topical gels used once daily in the management of acne vulgaris. Cutis. (2009)
  19. Nichols K, Desai N, Lebwohl MG. Effective sunscreen ingredients and cutaneous irritation in patients with rosacea. Cutis. (1998)
  20. Short RW, et. al. Effects of moisturization on epidermal homeostasis and differentiation. Clin Exp Dermatol. (2007)
  21. Bowring AR, Mackay D, Taylor FR. The treatment of napkin dermatitis: a double-blind comparison of two steroid-antibiotic combinations. Pharmatherapeutica. (1984)
  22. Hengge UR. Topical, Non-Medicated LOYON® in Facilitating the Removal of Scaling in Infants and Children with Cradle Cap: a Proof-of-Concept Pilot Study. Dermatol Ther (Heidelb). (2014)
  23. Beeckman D, et. al. A 3-in-1 perineal care washcloth impregnated with dimethicone 3% versus water and pH neutral soap to prevent and treat incontinence-associated dermatitis: a randomized, controlled clinical trial. J Wound Ostomy Continence Nurs. (2011)
  24. Fowler JF Jr. Efficacy of a skin-protective foam in the treatment of chronic hand dermatitis. Am J Contact Dermat. (2000)
  25. Zhai H, et. al. A bioengineering study on the efficacy of a skin protectant lotion in preventing SLS-induced dermatitis. Skin Res Technol. (2000)
  26. Saary J, et. al. A systematic review of contact dermatitis treatment and prevention. J Am Acad Dermatol. (2005)
  27. Pellicoro C, Marsella R, Ahrens K. Pilot study to evaluate the effect of topical dimethicone on clinical signs and skin barrier function in dogs with naturally occurring atopic dermatitis. Vet Med Int. (2013)
  28. Palmieri B, Gozzi G, Palmieri G. Vitamin E added silicone gel sheets for treatment of hypertrophic scars and keloids. Int J Dermatol. (1995)
  29. Burgess IF, Brown CM, Lee PN. Treatment of head louse infestation with 4% dimeticone lotion: randomised controlled equivalence trial. BMJ. (2005)
  30. Oliveira FA, Speare R, Heukelbach J. High in vitro efficacy of Nyda L, a pediculicide containing dimeticone. J Eur Acad Dermatol Venereol. (2007)
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  32. Heukelbach J, et. al. A highly efficacious pediculicide based on dimeticone: randomized observer blinded comparative trial. BMC Infect Dis. (2008)
  33. Heukelbach J, et. al. A new two-phase dimeticone pediculicide shows high efficacy in a comparative bioassay. BMC Dermatol. (2009)
  34. Burgess IF, Brunton ER, Burgess NA. Single application of 4% dimeticone liquid gel versus two applications of 1% permethrin creme rinse for treatment of head louse infestation: a randomised controlled trial. BMC Dermatol. (2013)
  35. Richling I, Böckeler W. Lethal effects of treatment with a special dimeticone formula on head lice and house crickets (Orthoptera, Ensifera: Acheta domestica and Anoplura, phthiraptera: Pediculus humanus). Insights into physical mechanisms. Arzneimittelforschung. (2008)
  36. Burgess IF. The mode of action of dimeticone 4% lotion against head lice, Pediculus capitis. BMC Pharmacol. (2009)
  37. Heukelbach J, et. al. Ovicidal efficacy of high concentration dimeticone: a new era of head lice treatment. J Am Acad Dermatol. (2011)
  38. Gallardo A, et. al. Comparative efficacy of new commercial pediculicides against adults and eggs of Pediculus humanus capitis (head lice). Parasitol Res. (2012)
  39. Strycharz JP, et. al. Ovicidal response of NYDA formulations on the human head louse (Anoplura: Pediculidae) using a hair tuft bioassay. J Med Entomol. (2012)
  40. Ortega-Insaurralde I, et. al. Influence of the formulations in removing eggs of Pediculus humanus capitis (Phthiraptera: Pediculidae). Parasitol Res. (2014)
  41. Becker LC, et. al. Safety Assessment of Dimethicone Crosspolymers as Used in Cosmetics. Int J Toxicol. (2014)