![]() Conditions that affect the nervous system, such as Parkinson’s disease or Alzheimer’s disease.Radiation for treatment of head and neck cancers.Numerous medications, including some common antibiotics and antihistamines.Exposure to certain chemicals, such as insecticides and solvents.Sinus and other upper respiratory infections.Most people who develop a smell disorder have experienced a recent illness or injury. Smell disorders have many causes, with some more obvious than others. Phantosmia is the sensation of an odor that isn’t there.Parosmia is a change in the normal perception of odors, such as when the smell of something familiar is distorted, or when something that normally smells pleasant now smells foul.In rare cases, someone may be born without a sense of smell, a condition called congenital anosmia. Anosmia is the complete inability to detect odors.Hyposmia is a reduced ability to detect odors.People who have a smell disorders either have a decrease in their ability to smell or changes in the way they perceive odors. These nerve endings help you sense irritating substances-such as the tear-inducing power of an onion-or the refreshing coolness of menthol. This sense involves thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth, and throat. Your sense of smell is also influenced by something called the common chemical sense. Some people who go to the doctor because they think they’ve lost their sense of taste are surprised to learn that they’ve lost their sense of smell instead. Without smell, foods tend to taste bland and have little or no flavor. ![]() Without the olfactory sensory neurons, familiar flavors such as chocolate or oranges would be hard to distinguish. In this way, your senses of smell and taste work closely together. As a result, you lose much of your ability to enjoy a food’s flavor. If the channel is blocked, such as when your nose is stuffed up by a cold or flu, odors can’t reach the sensory cells that are stimulated by smells. Chewing food releases aromas that access the olfactory sensory neurons through the second channel. The second pathway is through a channel that connects the roof of the throat to the nose. The first pathway is through your nostrils. Smells reach the olfactory sensory neurons through two pathways. These representations are registered by the brain as a particular smell. There are more smells in the environment than there are receptors, and any given molecule may stimulate a combination of receptors, creating a unique representation in the brain. Once the neurons detect the molecules, they send messages to your brain, which identifies the smell. Microscopic molecules released by substances around us-whether it’s coffee brewing or pine trees in a forest-stimulate these receptors. Each olfactory neuron has one odor receptor. These cells connect directly to the brain. Your ability to smell comes from specialized sensory cells, called olfactory sensory neurons, which are found in a small patch of tissue high inside the nose. Your sense of smell-like your sense of taste-is part of your chemosensory system, or the chemical senses. To learn more about your sense of taste, and how it relates to your sense of smell, read the NIDCD's Taste Disorders publication. Many people who have smell disorders also notice problems with their sense of taste. In one study, nearly one-quarter of men ages 60–69 had a smell disorder, while about 11 percent of women in that age range reported a problem. Problems with the sense of smell increase as people get older, and they are more common in men than women. One to two percent of North Americans report problems with their sense of smell. It can also be a sign of more serious health problems. Any loss in your sense of smell can have a negative effect on your quality of life. Your sense of smell is also a warning system, alerting you to danger signals such as a gas leak, spoiled food, or a fire. You may delight in the aromas of your favorite foods or the fragrance of flowers. Your sense of smell helps you enjoy life.
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