Smell and Taste Perception

Taste and smell are two important senses. To smell, odors must reach the olfactory nerves in the roof of the nasal passages. The sensations are converted into electrical signals and sent to the brain for processing and recognition. Taste occurs when molecules in food stimulate gustatory cells in the taste buds located over the tongue, roof of the mouth and throat. The taste buds are grouped in clusters designed to pick up at least one of the five known tastes: sweet, sour, bitter, salty and umami (savory).

Taste and smell are senses that are closely linked. While taste buds are attributed to specific types of tastes, it’s really the sense of smell that helps us recognize the “flavor” of food and drinks.

Smell Sense and Taste Loss

As we age, the sense of smell becomes less acute. Researchers estimate about 60 to 75 percent of people over 80 have significant smell impairment. Taste perception declines also, but not to the same degree. But because taste is so dependent upon smell, the loss of smell can greatly interfere with the ability to taste. In one study, more than 50 percent of patients with smell problems reported having changes in taste. 45 percent of the participants said they enjoyed eating less because of the taste changes.

In addition to smell problems, some other potential causes of changes in taste include: upper respiratory infection, middle ear infection, head injury, radiation therapy to the head and neck, use of certain medications, exposure to some types of chemicals, dental problems and chewing problems.

Pine Mouth

Pine nuts are the edible seeds of pine trees. The small ivory colored seeds have a sweet, buttery flavor and are often used to make pesto or are toasted for a salad topping. Over the past year or so, some have reported temporary, unexpected changes in taste associated with eating pine nuts. Specifically, people complain of the development of a metallic or off-taste that lasts for up to two weeks. The symptoms are referred to as “pine mouth” and, so far, seem to only be associated with imported Chinese pine nuts.

Doctors know very little about pine mouth and don’t understand why people are developing the taste problems. Cases seem to be sporadic and patients are finding about the problem by a flurry of reports over the internet. Complicating the investigation is the fact that only some develop the symptoms. Others eating from the same batch of pine nuts don’t develop any taste problems.

Some people theorize the taste problems could be a symptom of an allergy to pine nuts. For some people, pine nuts can cause a severe, life-threatening allergic reaction. Thus the FDA requires them to be listed on package labels if they are part of a product’s ingredients. Richard Doty, Ph.D., Smell and Taste Researcher with the University of Pennsylvania School of Medicine, says, in susceptible people, pine nuts may cause enough of an allergic reaction to inflame the olfactory (smell) system. Even a very small level of inflammation (too small to be detected with standard examination) can affect a person’s ability to smell properly and perceive flavor. In Europe, health officials have tested pine nuts and have not found any detectable traces of chemicals or contaminants that could potentially cause the metallic taste.

While the exact cause of “pine mouth” remains elusive, the good news is that the taste alteration seems to only be temporary. Most people return to normal taste perception within two weeks. People may be able to prevent the symptoms by avoiding pine nuts or purchasing European pine nuts. Although the European pine nuts are much more expensive, so far, they have not been linked to “pine mouth.”

For general information on smell and taste problems:

American Academy of Otolaryngology – Head and Neck Surgery

American Rhinologic Society

National Institute on Deafness and Other Communication Disorders