This is the third in a series on dementia and the senses. Today we discuss smell. (This is an adaptation of a post originally wrote a few years ago.)

As I write this, it’s a gorgeous early fall day. I am sitting in our living room with the windows open. College football is on TV. There are a couple of candles burning…one in the kitchen and one in the bathroom.

Our ancient mastiff, Karl, is curled up in a tiny chair in typical Karl-fashion. Our 20-pound mutt, Gus-Gus, is sitting on my arm as I type. I’m so used to him being in this position that I barely notice how hard it is to navigate the keyboard. The cats have found a sun puddle to share.

I can hear our neighbor guy mowing his yard. He is retired, and he probably devotes 20 hours a week to his lawn. There is an odor in the air that tells me another neighbor must be grilling.

It’s cool enough that I’m wearing a sweatshirt, but warm enough that I’ve got on basketball shorts. I just heated up some canned soup for lunch. As I usually do, I added oyster crackers. A ridiculous amount of oyster crackers. I like the crunch and the saltiness.

It’s a good day.

It’s a good day because I am able to experience the world through sight, sound, taste, smell, and touch. Our experience of the world is based on those five senses, and our feelings and actions are based on this experience.

This makes me think about how dementia changes one’s experience of the world…and how it might impact smell, in particular.

It is true that our sense of smell declines as we age. Many people will notice that as they get older they can no longer detect smells like they may have been able to in the past. However, the change that occurs for individuals with dementia is more severe and can even be dangerous.

Smell has an important function for us. It helps us to detect danger. People with dementia may lose the ability to interpret certain smells as signs of danger.

A few nights ago, I put a couple pieces of leftover pizza in the oven. Then I got busy putting away laundry and forgot about the pizza. You know what alerted me to the burning pizza? The smell of burning pizza.

People with dementia may also forget that they put something in the oven. However, they may not be alerted to a problem by the smell of food burning. They may even turn off a smoke detector because they think it is malfunctioning.

Smoke alerts us to fire…that connection is eventually lost for people with dementia.

Smell also alerts us to spoiled food. You go out to eat. You put your leftovers in the fridge. You forget about them–until something in your fridge start smelling like death a week later. You remember the leftovers. You take them directly to the trash can outside because if you put them in the kitchen trash your whole house will stink.

It doesn’t work that way for people as dementia progresses. It may not be that you cannot smell the odor of your leftovers. It’s just that you don’t interpret that smell as problematic. Your nose doesn’t shrivel up to make what is sometimes called “stank face.” You find the food from last week. You don’t remember when you went out to eat. You’re just excited you have something to eat for dinner. It isn’t rare for someone with dementia to experience food poisoning because they’ve eaten rotten food.

Unfortunately, it’s also not rare for someone with dementia to drink a liquid like bleach. If I tried to drink bleach, my nose would alert me to a problem before the bleach got to my mouth. My brain would immediately send out an “abort” message. However, the dementia brain may be unable to relay that message. I’ve known people with dementia who have tried to drink Clorox bleach, Pine Sol, laundry detergent, and glue. The chemical smell of these liquids didn’t trigger a danger warning.

You may not realize it, but the nose of a typical person does a routine sniff test of anything we want to put in our mouths. It sends a warning to the brain if something isn’t quite right. The dementia brain drops the ball on this.

Our sense of smell also alerts us to problems with our own hygiene. I’m gonna admit something here…I sometimes wear clothes more than once before I wash them. I take off items of clothing at the end of the day and must decide whether they go back in the closet or in the dirty clothes pile. (For me, this is especially true for jeans because they become more comfortable after multiple wearings.) You know how I make that decision? I smell the clothes. If I can still faintly smell laundry detergent, they go back in the closet.

A person with dementia might take off their clothes at the end of the day and throw them on top of the dresser. In the morning, they find some clothes on the top of the dresser and put them on. They may remember they wore these clothes the day before–or they may not. Maybe they do this for several days in a row. And then a family member comes to visit and asks, “What’s that awful smell?” The person with dementia isn’t bothered by the odor, so they are offended and angered by the question.

A woman I know was checking in on her mother, who was in the early stages of dementia and lived alone. She hadn’t visited for several days. When she walked in, the smell of urine was overwhelming. She went on a hunt to find the source of the odor. She found several pairs of wet underwear wadded up under the bed. Her mother, oblivious to the offensiveness of smell, couldn’t tell her how they got there. It’s likely she was so embarrassed about not making it to the bathroom that she decided to hide the evidence.

My husband and I have three dogs and two cats. Every once in a while, once of us smells…something. Maybe it’s the smell of pet urine. Maybe it’s feces. The instant we smell that, we are on the hunt to find the source. The smell is so offensive to us that we stop whatever we are doing to take care of it. It’s urgent.

People with dementia, even if they do smell those pet odors, may not be interpreting them as problematic. It’s not unusual that people with dementia forget to clean the litterbox or don’t pick up dog poop on the kitchen floor. Why? Because they aren’t motivated into action by the smell. Obviously, this can create unsanitary and unsafe conditions.

Keep in mind that our actions are based on how we experience the world. Dementia alters those experiences by changing our sensory perceptions. When people with dementia do something that seems illogical to us, it is often because those are logical actions based on their experience.

And those experiences are based on what they do and do not taste, see, hear, touch, and smell.