Exposure
Routes of Exposure
There must be exposure to substances before they can cause adverse effects. There are many exposure factors that play a role in how chemicals impact health. Fragrance chemicals can enter the body via numerous routes.
SKIN
The skin is the most studied route of exposure to fragrance. Until the 1970s the
skin was thought to be an effective barrier to fragrance chemicals entering the
body. Most research focused on how fragrance affected the skin. There was little
focus on materials being absorbed from the skin into the body. It was then
discovered that not only did fragrance chemicals enter the body through the
skin, but significant amounts could be absorbed. Materials absorbed through the
skin could have toxic systemic effects.
How much of a material is absorbed through the skin depends on numerous factors. In general, large molecules are not readily absorbed into the skin and materials must have some fat solubility to be absorbed. Materials in mixtures may absorb differently than single materials. The concentration of the material, length of exposure, condition and location of the skin also play vital roles in absorption. Moisture and heat also increase absorption. Logically the larger the area of exposure, the more material will be absorbed. Areas that are covered or occluded after application may absorb more than included areas.
Perfumes and colognes are often applied to the skin. These products represent only a fraction of the exposures to fragrance. Soaps, lotions and other toiletries have contact with large areas of the body. Clothing washed in scented products have direct contact and cover large areas of skin. There is often prolonged skin contact with cleaners in the presence of moisture and heat. Multiple scented products come in contact with the skin on a daily basis.
Some fragrance materials are readily absorbed through the skin, while other are not. Testing shows coumarin is well absorbed through the skin at 60% while only about 3% of limonene is absorbed. However, other studies have shown that limonene disrupts the normal protective mechanisms of the skin and causes increased absorption of other materials into the skin. Mixtures will absorb differently than singular materials.
Materials that are absorbed through the skin not be immediately dispersed. The skin can act as a reservoir. The material may then be slowly released into systemic circulation. There can be continued systemic exposure long after the initial contact. Some materials enter systemic circulation quickly, while others may remain in the skin reservoir much longer. Once the materials are in the skin, they may be metabolized and broken down. Not all materials can be metabolized in the skin and remain relatively intact. Systemic exposure may be to the original substance or to the broken down compounds.
Fragrance materials that cause allergies do so by mechanisms that are a bit different than allergies due to pollen, dander, and other protein based allergens. Allergies to protein based substances occur when the body perceives these materials as harmful and defense mechanisms are triggered. Fragrance chemicals are not usually protein based and are usually considered too small to be detected as an allergen. However, some of these materials act as a hapten and bind with proteins in the skin. The proteins in the skin are modified by the haptens and the body then treats these proteins as a foreign substance and allergic reactions are triggered.
Once such sensitization occurs, the only way to prevent allergic reactions is to avoid exposures. Unlike other allergies, those caused by haptens do not generally respond to allergy medications. Such allergies also tend to last a lifetime.
Exposure to the Brain Via Olfactory Pathways
In order for odors to be detected, materials must be airborne. As air passes over olfactory receptors in the nose stimuli is sent via olfactory pathways to the brain. In order for odors to be detected, they must have certain characteristics. They must be fat soluble and have some degree of water solubility. The molecules must be relatively small, with a molecular weight of less than 300.
The olfactory receptors are stimulated and the nerve impulses travel via the olfactory nerve to the areas of the brain where the impulses are interpreted. Odors trigger both psychological and physiological responses. It has been shown that inhaling fragrance compounds stimulates both changes in emotions and autonomic nervous system parameters such as blood pressure and pulse.
IIn addition to transmitting odor stimuli, the olfactory pathways also serve as an entry point for toxic materials into the brain.
Links to related information:
OlfactionChirality & Odour Perception
Olfactory Pathways as Entry Point to the Nervous System