|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|
Functions as both an occlusive and as an emollient. More hydrating than petrolatum, but less so than glycerin.
Useful in treating contact dermatitis, hand dermatitis, diaper dermatitis and incontinence-associated dermatitis.
Dimethicone gel sheets can be used together with topical vitamin E to treat hypertropic scars and keloids.
Has a weak effect on restoring the epidermal barrier, probably by stimulating keratinocyte proliferation.
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Table of contents:
Dimethicone, also known as polydimethylsiloxane (PDMS), is a fluid mixture of fully methylated linear siloxane polymers end-blocked with trimethylsiloxy units. It is used extensively in cosmetic formulations as a conditioning agent, skin protectant and moisturizer. It also influences the sensory properties and hence the skin feel of cosmetic formulations.
Clinical and animal studies have reported that dimethicone is not absorbed following dermal exposure. Dimethicone does not alter the phase-transition temperatures and enthalpies of the stratum corneum lipids and therefore does not act as a penetration enhancer. 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.
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. It has both occlusive and emollient properties, which means that it can physically block transepidermal water loss (TEWL) in the stratum corneum as well as make the skin smooth and soft to the touch by filling in the spaces between desquamating corneocytes. In one study, it was found to have greater hydration potential than petrolatum, but to be less hydrating than glycerin.
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.
3.2 Improved barrier function
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. 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. Treatment satisfaction was also higher, 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.
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.
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. 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.
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.
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. 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.
More convincingly, a systematic review of contact dermatitis treatment and prevention has also concluded that barrier creams containing dimethicone can prevent irritant contact dermatitis.
However, dimethicone-containing products appear to be less effective at protecting the skin from insults or maceration than petrolatum-containing products. 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.
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
3.5 Treatment of head lice
Numerous clinical trials have established the efficacy of dimethicone-based formulations in clearing head louse infestations. Its mode of action is physical; it exerts its lethal effects by displacing air in the tracheal system of the head. This inhibits water excretion, which causes physiological stress and eventually death either through prolonged immobilisation or the rupture of the gut.
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.
4.2 No evidence of genotoxicity
Dimethicone was negative in all genotoxicity assays, including an oral and dermal dose carcinogenicity test on mice.
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