Physiological effect of olfactory stimuli inhalation in humans: an overview.

The importance of odorants in human life has long been recognized. Literature contains different approaches of physiological and psychological effects of odorant compounds, fragrances and essential oils. This work discusses odorants inhalation effect, based on an overview of major studies in humans. Beneficial effect of fragrances is mainly related to human behaviour. Studies document odorants influence in sympathetic and parasympathetic nervous systems, and neurophysiological brain activity. Moreover, odours compounds can act on the neuroendocrine system, neurotransmitters and neuromodulators, influencing psychological behaviour as well as body function. Odorant inhalation modulates physiological pathways, and in some cases, results in skin function regulation. The mechanism is incompletely elucidated. These findings suggest that olfactory system plays a role in central nervous system function beyond that of smell. In this overview, it was observed that odour compounds influenced stress biomarkers, dehydroepiandrosterone, oxidative stress, estradiol, dopamine, cutaneous barrier, sebum secretion and cutaneous immune system in humans. Some can be related with skin function. As the skin is associated with an extensive biochemical cascade and has complex mechanisms, studies have far to go, as there are processes not yet investigated related to skin that may be affected through olfaction. Future researches are needed to further understand and describe the mechanisms of action of physiological effects in fragrance compounds.

Chlorothalonil, a possible cause of erythema dyschromicum perstans (ashy dermatitis).

We studied 39 patients with erythema-dyschromicum-perstans-like dermatitis seen at Changuinola Hospital in Panama. They were compared with 41 controls. The 2 groups were native field workers of the banana plantations exposed to many pesticides. In 34 patients, there was a positive patch test reaction to 2,4,5,6-1,3-tetrachloroisophthalonilnitrile (chlorothalonil, TCPN) 0.001% in acetone. In 39 cases, biopsies showed a lichenoid tissue reaction compatible with a chronic pigmented dermatitis or erythema-dyschromicum-perstans-like dermatitis. Chlorothalonil is possibly the cause of the pigmented dermatitis observed in the 39 banana farm workers studied. Until additional studies are carried out, we consider this a possible rather than definite cause-and-effect relationship.

In vivo biophysical characterization of skin physiological differences in races.

The role of race in modulating skin responses has been investigated. Several parameters (skin thickness, transepidermal water loss, water content of the stratum corneum and skin biomechanics) have been measured using noninvasive tools in whites, Hispanics and blacks to assess whether the melanin content could induce changes in skin biophysical properties. Marked differences between races appear in stratum corneum water content and in skin extensibility, recovery and elastic modulus. Measurements done in different sun-exposed sites highlight the effects of solar irradiation on the skin and the role of melanin in preventing skin damage. The study shows that racial differences in skin physiology exist and are mainly related to the protective role of melanin present in races with darker skin. Moreover, differences in skin hydration are not fully explained according to the site and presence of hair.

Animal models of percutaneous penetration: comparison between Mexican hairless dogs and man.

In an attempt to find better animal models for percutaneous penetration studies relevant to man, urinary excretion of 14C-labeled compounds was studied in the Mexican hairless dog and in man. With benzoic acid, progesterone and testosterone, the total absorption and maximum absorption rate were greater in man than in the hairless dog. As urinary excretion lasted days longer in the dog than in man, it is possible that the thin dog skin held the chemicals longer than man. Surface-counting experiments with a Geiger counter with a thin mica window protected by a special screen of fine stainless steel wires showed that benzoic acid and progesterone did persist on the dog skin far longer than on human skin. We conclude that the Mexican hairless dog has permeability characteristics significantly different from those of human skin.