Occlusion effect

Ointments are the most effective formulations for psoriasis because they have an occlusive oily phase that conveys a hydrating effect and enhances penetration of the corticosteroid into the dermis. They are not suited for use in the axilla, groin, or other intertriginous areas where maceration and folliculitis may develop secondary to the occlusive effect. 

In contrast, vehicle that are immiscible with water and those with a high proportion of oils have occlusive effects. They reduce both insensible perspiration and the release of sweat. The sweat collects as droplets at the opening of the glands, but does not spread as a film between the hydrophobic skin surface and the hpophific base because the free surface energy of the vehicle-skin interface is smaller than that between water and skin. If a lipophilic layer of vehicle is present, this is not spontaneously replaced by the water-skin layer if sweat is secreted. 

Following the evaporation of water from the lipid nanodispersion applied to the skin surface, lipid particles form an adhesive layer, applying occlusion to the surface [17,40]. Therefore, the hydration of the stratum comeum may increase, which can facilitate drug penetration into deeper skin strata and even systemic availability of the drug. Occlusive effects are strongly related to particle size. Nanoparticles have turned out 15-fold more occlusive than microparticles [17], and particles smaller than 400 nm in a dispersion containing at least 35% high-crystallinity lipid proved to be most potent [41]. 

Vehicles - Ointments are more occlusive and are preferred for dry scaly lesions. Use creams on oozing lesions or in intertriginous areas where the occlusive effects of ointments may cause maceration and folliculitis. 

Striae rubrae distensae, mainly in the inguinal and axillary regions (occlusion effect)... 

HP3 is of questionable physiological significance. As expected, in both in vitro and in vivo models, a strong occlusion was seen after application of white petrolatum. This strong occlusive effect as observed with the lipophilic pastes led to a diminution of the TEWL because of the concomitant increase in the barrier function of the stratum corneum and despite an accumulation of moisture in the horny layer. This justifies the use of such pastes for skin protection, but not for drying the skin. 

Not only were these shown to significantly absorb water in vitro, but they lack a significant occlusive effect which is detrimental in a situation where water evaporation should not be impaired. 

The TEWL measurement has been a valuable tool in barrier repair experiments where repair kinetics were followed by TEWL. However, there are some problems with this method when the efficacy of moisturizers is to be evaluated. Some ingredients of moisturizers like petrolatum are shown to be occlusive.8 Therefore TEWL readings might reflect the occlusive effect of the cream, rather than an improved, less permeable SC. Measurements performed shortly after application of the moisturizer may represent surface water loss of residual emulsion water instead of TEWL. The TEWL measurements must be performed in an environmental chamber with constant temperature and humidity after an appropriate rest period in order to minimize the contribution of sweat gland activity.9... 

Occlusion of the skin, seen with application of water-impermeable drug vehicles or patches, alters the rate and extent of toxicant absorption. As the skin hydrates, a threshold is reached where transdermal flux dramatically increases (approximately 80% relative humidity). When the skin becomes fully hydrated under occlusive conditions, flux can be dramatically increased. This occlusive effect must be accounted for when extrapolating toxicology studies conducted under occlusive conditions to field scenarios where the ambient environmental conditions are present. Hydration may also markedly affect the pH of the skin, which varies between 4.2 and 7.3. Therefore, dose alone is often not a sufficient metric to describe topical doses when the method of application and surface area become controlling factors. Dose must be expressed as mg/cm2 of exposed skin. 

Maceration of skin caused by inhibition of skin breathing The transpiration of water vapor is greatly inhibited in the presence of PSA on the skin. It may cause skin maceration and folliculitis. However, this occlusive effect is important for enhancing drug permeation, which is called occlusion effect. 

Gels and creams are generally easier to apply to animals but are less occlusive than ointments. Ointments provide a longer duration of drug action, and the occlusive effect may enhance preparation of the active ingredi-ent(s) to the site of infection. 

The therapeutic effectiveness of topically applied corticosteroids is attributed primarily to their antiinflammatory activity. The relative efficacy of topical corticosteroids appears to be in the following order hydrocortisone, prednisolone, betamethasone < hydrocortisone valerate or butyrate, betamethasone valerate, triamcinolone acetonide, flucinolone acetonide < betamethasone dipropionate, fluocino-nide. In addition to the nature of the corticosteroid, its solubility, and, to a lesser extent, the concentration used, clinical efficacy is influenced by the formulation of the preparation. Glucocorticoids appear to have greater efficacy when formulated in ointment bases than in cream or lotion vehicles. This could be attributed to the occlusive effect provided by ointments. The application of an occlusive dressing further enhances penetration and persistence of the steroid (reservoir effect) in the stratum corneum. " ... 

Cevc G, Mazgareanu S, Rother M, Vierl U (2008) Occlusion effect on transcutaneous NSAID delivery from conventional and carrier-based formulations. Int J Pharm 359(1-2) 190-197... 

At concentrations above 2% salicylic acid has a keratolytic effect, causing the keratin layer of the skin to shed. Keratolysis is achieved by increasing the hydration of the stratum corneum, softening the cells and facilitating dissolution of the intracellular cement that bonds the cells together so that they separate and detach (desquamate). Moisture is essential to this process and is provided by either the water in the formulation or the occlusive effect produced by its application to the skin. 

PEPE (perfluoro polymethyl isopropyl ether) this is a filmogenic polymer that protects the skin without any occlusive effect. 

Smith, G., and Lawson, D. D., Experimental coronary occlusion effects of the administration of oxygen under pressure. Scot. Med. J. 3, 346-350 (1958). 

Using enteral feeding tubes to deliver drugs is a common practice. It offers an alternative to parenteral administration in patients unable to take drugs by the oral route. However, in addition to complications of tube occlusion, effects on drug bioavailability and other potential interactions need to be considered when using this route. Medications... 

T Agner, J Serup. Time course of occlusive effects on skin evaluated by measurement of transepidermal water loss (TEWL). Contact Dermatitis 28 6-9, 1993. 

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