Why Do I Have Crust In My Eyes?

A while back one morning, my son came wandering out into the living room rubbing his eyes and complaining that they felt funny. So I had him sit on the couch, and had a look. “Well, you’ve got some crust in your eyes,” I said, starting to (carefully) pull it off his eyelids.

“Why do I have crust in my eyes?” he asked.

“You know,” I answered, “I don’t know.” And I really don’t. I mean I’ve had it, you’ve had it, we’ve all had it. Usually just from normal sleep, when you wake up with dried little eye booger nuggets on your lashes. The worst I ever got it was the time I came down with conjunctivitis in college, and had to apply a damp cloth to my eye for several minutes in order to rehydrate the crust enough to [i]open my eye[/i] – a slightly terrifying experience, let me tell you. But I never gave it much thought, beyond assuming it was dried tears mixed with dirt, or mucous, or the like.

Kids. They make you think.

What is this eye crust stuff?

Eye crust, also known as “sleep” or rheum, is “a combination of mucus, oil, skin cells and other debris that accumulates in the corner of your eye while you sleep. It can be wet and sticky or dry and crusty, depending on how much of the liquid in the discharge has evaporated”. Which means that, for a change, my initial guess was correct. It’s dried “eye boogers”.

Wait, mucus? I thought that was a nose and/or sinus thing?

To tell the truth, so did I. Mostly, if pressed I’d have defined “mucus” as “that stuff I cough up, choke on, and sneeze out when I’m sick”. It certainly wouldn’t have associated it with eyes. So, what is mucus? Well, according to MedicineNet.com, mucus is “a normal, slippery and stringy fluid substance produced by many lining tissues in the body. It is essential for body function and acts as a protective and moisturizing layer to keep critical organs from drying out. Mucus also acts as a trap for irritants like dust, smoke, or bacteria. It contains antibodies and bacteria-killing enzymes to help fight off infections.”

The article also notes that on average our bodies produce between 1 and 1.5 liters (roughly 4 to 6.25 cups) of mucus per day and says that we “don’t tend to notice mucus at all unless its production is increased or the quality of mucus has changed, as may happen with different illnesses and conditions.”

So, yeah. That’s a lot of mucus.

Eye Mucus

Technically, eye mucus is called “mucins”, and are produced by the conjunctiva, a thin, semi=transparent mucus membrane (much like the membranes that line your nose and sinuses) that covers the white of the eyeball (known formally as the sclera).


The mucins work with tears to keep the eye moist and lubricated, so that you don’t scratch your eye up simply by blinking or looking around.

Should I be concerned about my eye crust?

Generally speaking, no. It’s a perfectly normal thing, caused by your tear ducts and conjunctiva [i]doing their jobs[/i] and then by evaporation. It might be a little uncomfortable to clean out once in a while, but as long as you don’t drive it into your eyeball and scratch things up the crust isn’t an issue.


It can be an indicator of problems, though. Particularly if abnormally thick crust or discharge is combined with green, white, or yellow eye mucus. This can be a sign of such things as conjunctivitis, blepharitis, a stye, or a corneal ulcer or a blocked tear duct. In this case you should see your family doctor for a diagnosis and treatment. You don’t want to be taking chances with your eyes.

Lovely. Anything else?

Yeah. Have you ever woken up with a crust at the corner of your mouth? That’s also rheum.


Why’s it called a “Bobcat”?

Our HOA is tearing up and repairing the parking lots in my complex this week, forcing me to park at a distance from my condo. Yesterday, after getting home from kindergarten, my son saw this parked in front of our building:

“What’s that?” he asks, excited.

“It’s a bobcat,” I answer.

“That’s silly,” he tells me. Then he thinks for a moment.  “Why’s it called a bobcat?”

“It…” I begin, and then I stop. “You know what?”

“What?” he asks.

“I don’t know why.”

Why is it called a “Bobcat”?

This turns out to have an extremely simple answer.  The machine is one of a number of vehicles manufactured by the Bobcat Company,  Bobcat started in North Dakota in 1947 and still has their headquarters and three production facilities in that state.  Other production facilities are found in France, the Czech Republic, and China.  They were acquired by Doosan Infracore, a South Korean conglomerate, in 2007.  The machines are called “Bobcats” for the same reason that trucks built by Chevrolet are called “Chevys”.

What is that particular machine in the picture?

The machine in the foreground is a Bobcat S650 Skid-Steer Loader, while the one in back (mostly obscured by the S650) is a Bobcat S250 Skid-Steer Loader – a discontinued Bobcat model.  Here’s a better picture of one:


…Skid-Steer Loader?

Yeah.  Here’s how Wikipedia explains the process that gives them their name:

Skid-steer loaders are typically four-wheel vehicles with the wheels mechanically locked in synchronization on each side, and the left-side drive wheels can be driven independently of the right-side drive wheels. The wheels typically have no separate steering mechanism and hold a fixed straight alignment on the body of the machine. By operating the left and right wheel pairs at different speeds, the machine turns by skidding, or dragging its fixed-orientation wheels across the ground. The extremely rigid frame and strong wheel bearings prevent the torsional forces caused by this dragging motion from damaging the machine.

In other words, they turn like tanks.  And the skid-steer process allows them to turn without moving forward, because the left wheel pair can go forward and the right wheel pair can go backwards (or vice versa), making them able to work in cramped conditions.

What are crab apples?

One one end of my son’s kindergarten is a tall, spreading tree that’s been bearing little green apples for a while now.  Just about every day we contemplate this tree, because he passes it on the way around the back of the building to wave goodbye to his friends.  One one particular day, though, he stopped to really look at the tree.  And at the little green apples covering the ground around the trunk.  Then he stoops and picks one up.  “Can I take this home?” he asks.

I’m not surprised by the questions.  He’s five, after all.  He collects things.  Rocks.  Acorns.  Sticks.  Anything that catches his eye as interesting or unusual or just fun.  All of it comes home with him, sometimes to end up in his “treasure box” and sometimes to be quietly disposed of by mommy and daddy.  “No,” I tell him.  “They’re yucky.”

He nods sagely at that.  “And poisonous?” he asks, voice half worried and half hopeful.

“I don’t think so,” I tell him.  “But don’t eat one.  They don’t taste good.”  I say that with confidence, although I’ve never actually tried to eat one.

He tosses the apple aside.  “Well,” he declares with confidence, “I think they’re poisonous.”  Then he looks at the tree again.  “Why do they grow it?”

I shrug.  “Because it looks nice.”

Crab Apple Trees

Crab apple trees (also known as “crabapple trees” and “wild apple trees” are one of between 30 and 55 (depending on how  you classify them) species of the genus Malus, making them close relatives of the domestic apple tree (Malus pumila) that provides the apples we eat.  They are small to medium trees, with five to ten petaled flowers (depending on species) that develop into fruit that is an average of two inches in diameter.  The fruit is edible and non-poisonous, but is often quite sour due to high concentrations of malic acid – the same acid that makes grapes ‘tangy’ and Sweetarts ‘sour’.

Why would we grow crabapples?

Reasons for cultivating crabapples vary.  You’ll find them planted as ornamental trees because the flowers (and even the fruit) and considered pretty and worth the effort of cleaning up the fallen fruit.  The small (for a tree) size also means they reach full size quickly (again, for a tree).  This makes them good choices for planting a wind break, or for use in small areas, or for planting when power lines may be overhead.

Crabapples don’t have a lot of commercial uses, as the fruit tends to be sour.  However, the fruit is a good source of pectin (used as a gelling and thickening agent) and the wood provides a pleasant smell when burned (and is one of the sources of “apple wood smoking”).  Also, some commercial apple farms plant crabapples to allow cross-pollination with domestic apples and to serve as rootstock when grafting limbs from prized apple trees.  I also found some claims that crabapple preserves are quite tasty and that adding some crabapple juice to apple cider adds an interesting flavor, but I can’t vouch for that – “interesting” can cover a lot of sins with food, after all.

So they have uses.  But that doesn’t mean my son can bring the crabapples home.

How Does Air Conditioning Work?

“The car is cold!” my son declares as he climbs in. “Good!”

It’s a hot day out, although not as hot as it’s been recently. Stil, the car’s pleasantly cool because I’d just parked it a few minutes ago so I could pick him up from Kindergarten, and the air conditioning had been running. “You’re right,” I agree.

“Why is it cold?” he asks.

“I had the air conditioning running,” I answer.

“Does it run all the time?” he asks, fastening his seatbelt.

“No,” I answer. “Only when I turn it on. You wouldn’t want it running in the winter, after all. When it’s cold out, you don’t want to make it colder.”

He nods at that, agreeing with the idea. “How does it make it cold?”

Uhm. “I… don’t know,” I answer, although I’ve got a vague idea in my head of how I think it works. Something to do with freon and fans, clearly. “I’ll have to find out.”

How do air conditioners work?

Air conditioners work, it turns out, for reasons very similar to the water cycle we all learned about as children. They have a liquid in them (the refrigerant) which absorbs heat from the environment (your house or car), evaporating into a gas in the process. This gas is warmer than it was as a liquid, but it’s still not hot. It gets hotter, though as it’s circulated into a compressor, a device designed to pressurize the gas back into a liquid. A side effect of this pressurization is heat (to see this yourself, try squeezing a rubber ball – the pressure generates heat).

The hot liquid is then passed into a condensor, where it goes through a radiator that allows the heat to dissipate. This works because, even if it’s really hot outside, the pressurized refridgerant is hotter. The cooler pressurized liquid is then passed through a narrow hole into the evaporator, where the pressure drops and the temperature drops along with it. Once it enters the evaporator, the whole cycle has started over.


This is an extremely simplified version of the process, of course. You can read a far more detailed explanation of air conditioning here.

Why does changing pressure make things hotter or colder?

According to Hyperphysics, heat is “energy in transit from a high temperature object to a lower temperature object. An object does not possess ‘heat’; the appropriate term for the microscopic energy in an object is internal energy. The internal energy may be increased by transferring energy to the object from a higher temperature (hotter) object – this is properly called heating.”

Internal energy is “defined as the energy associated with the random, disordered motion of molecules. It is separated in scale from the macroscopic ordered energy associated with moving objects; it refers to the invisible microscopic energy on the atomic and molecular scale.”

Now, let’s turn to the first law of thermodynamics, which states that “the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.” Based on this, it makes sense that increasing pressure increases internal energy and decreasing pressure decreases internal energy. Why? Because when you increase pressure you’re adding energy (because work is being done to the system), and when you decrease pressure you’re removing energy (because the system is working at pushing outwards). The added energy when you increase the pressure increases the internal energy that can be transferred to other systems, increasing the heat. Likewise, the decreased energy when you reduce the pressure reduces the internal energy that can be transferred to other systems.

What’s a system? The thing in question. The refrigerant in the air conditioner, for example, is a system for this purpose. So is the air in your home, or your car.

So, why does an air conditioner work? Thermodynamics, and clever engineering.

Why are there bugs in his hair?

My son attends a preschool, and we just found out that head lice are going around. This was a source of some concern for my son, because what he knows about it starts with “bugs in hair, bugs in hair!” and ends with “they make you itch!” So, naturally, he’s had some questions about them. Lots of questions. And, to tell the truth, so do I. Because I remember distinctly that, when I grew up, there was a social stigma associated with having lice. Not just because you had bugs in your hair, but because it meant you were perceived as filthy and dirty.

That’s hardly a fair assumption, of course. My son’s daycare and preschool is a wonderful place and they take hygene seriously. But it’s hard to shake beliefs that get ingrained during childhood. Also, it turns out that I know next to nothing about head lice. Beyond “bugs in hair, bugs in hair!”

What are head lice?


That picture up there? That’s a head louse – Pediculus humanus capitis – an obligate ectoparasite of humans, which is a fancy way of saying it’s a parasite that lives on human skin and needs to exploit a host as part of its life cycle. Pediculus humanus capitis feeds by biting the skin and injecting an anti-coagulant in order to suck blood (producing a dark red poop when digested), and generally colonizes the scalp (particularly the nape of the neck and the back of the ears).


According to the CDC,

The life cycle of the head louse has three stages: egg, nymph, and adult.

Eggs: Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets. Nits are laid by the adult female and are cemented at the base of the hair shaft nearest the scalp. They are 0.8 mm by 0.3 mm, oval and usually yellow to white. Nits take about 1 week to hatch (range 6 to 9 days). Viable eggs are usually located within 6 mm of the scalp.

Nymphs: The egg hatches to release a nymph. The nit shell then becomes a more visible dull yellow and remains attached to the hair shaft. The nymph looks like an adult head louse, but is about the size of a pinhead. Nymphs mature after three molts and become adults about 7 days after hatching.

Adults: The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white The number 5. In persons with dark hair, the adult louse will appear darker. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s head. To live, adult lice need to feed on blood several times daily. Without blood meals, the louse will die within 1 to 2 days off the host.[/quote]

Wikipedia expands on the definition of “nit” a little, stating that “the term nit refers to an egg without embryo or a dead egg”.

Pediculus humanus capitis requires anywhere from 8 to 24 days to mature from a newly-hatched nymph to a sexually mature adult, depending on temperature and access to blood. Once mature, a female can lay 3-4 eggs per day for pretty much rest of her life (which can be up to 30 days from hatching). This is under optimal conditions of course.

Ick. So, how does it spread?

Turning to the Centers for Disease Control once more,

Head lice are mainly spread by direct contact with the hair of an infested person. The most common way to get head lice is by head-to-head contact with a person who already has head lice. Such contact can be common among children during play at:

  •  school,
  • home, and
  • elsewhere (e.g., sports activities, playgrounds, camp, and slumber parties).

Uncommonly, transmission may occur by:

  • wearing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons worn by an infested person;
  • using infested combs, brushes or towels; or
  • lying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person.

Reliable data on how many people get head lice each year in the United States are not available; however, an estimated 6 million to 12 million infestations occur each year in the United States among children 3 to 11 years of age. Some studies suggest that girls get head lice more often than boys, probably due to more frequent head-to-head contact.

Interestingly, they note that (in the United States, at least) African-Americans are less likely to have an infestation than other races. They don’t quite know why, but speculate that the most common head louse in the United States is not well adapted to grasping the shape and width of some types of hair. Sadly, if you’re African-American and reading this, you can’t simply assume that you’re immune to head lice infestations. After all, “less likely” is not the same thing as “can’t get it”.

The CDC also states the following: “Head lice move by crawling; they cannot hop or fly. Head lice are spread by direct contact with the hair of an infested person. Anyone who comes in head-to-head contact with someone who already has head lice is at greatest risk. Spread by contact with clothing (such as hats, scarves, coats) or other personal items (such as combs, brushes, or towels) used by an infested person is uncommon. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.” To be safe, you probably still don’t want to share hats or combs or the like. But you should really avoid headbutting.

How do I know if I (or someone else) has lice?

Unsurprisingly, the CDC has a lot to say about this. Symptoms include:

  • Tickling feeling of something moving in the hair.
  • Itching, caused by an allergic reaction to the bites of the head louse.
  • Irritability and difficulty sleeping; head lice are most active in the dark.
  • Sores on the head caused by scratching. These sores can sometimes become infected with bacteria found on the person’s skin.

However, they also note that “Misdiagnosis of head lice infestation is common. The diagnosis of head lice infestation is best made by finding a live nymph or adult louse on the scalp or hair of a person…. If crawling lice are not seen, finding nits attached firmly within ¼ inch of the base of hair shafts suggests, but does not confirm, the person is infested. Nits frequently are seen on hair behind the ears and near the back of the neck. Nits that are attached more than ¼ inch from the base of the hair shaft are almost always non-viable (hatched or dead). Head lice and nits can be visible with the naked eye, although use of a magnifying lens may be necessary to find crawling lice or to identify a developing nymph inside a viable nit. Nits are often confused with other particles found in hair such as dandruff, hair spray droplets, and dirt particles.”

Yeah, that’s distinctly a bug. Now what?

Are you shocked to learn that the CDC has information on this as well? No? Me neither. The first thing that they recommend is, after confirming that someone in the household has an active infestation, you should check everyone else in the same household. It’s most likely to spread within a family, after all, as family members have the greatest odds of coming into head-to-head contact.

Pharmacologically speaking, you can use an over-the-counter or prescription medicine to kill the lice and nits. Be sure to follow the directions and, if the infested individual has long hair, consider more than one treatment. The CDC also recommends not re-washing hair for one to two days after treatment, to allow the residue of the medicine to continue to work. After treatment, comb the infested individual’s hair thoroughly to remove lice and nits and then check them around 8-12 hours after treatment. A few live but sluggish lice found during that time generally doesn’t mean that the treatment failed (some are more resistant than others), and you probably won’t need to retreat. If the lice are still active,, however, you may wish to use a different medicine and/or consult with a health care professional. Also, even after the lice appear gone, you should comb the hair with a nit comb every two to three days for the next two to three weeks to ensure the infestation is gone. Also, if the specific medicine you are using has different instructions, follow them.

Any clothing, bed linens, plush animals, etc that the infested individual came into contact with should be washed on hot (130 degrees F or higher) and then dried on the high heat cycle. Items that are not machine washable can be dry-cleaned instead, or sealed in plastic bags for two weeks. Vacuuming furniture and carpets can remove any lice that have fallen from the infested person, but they generally do not survive long off a human (since they are human-exclusive parasites that need human blood to live) so you don’t have to go to extreme measures to sterilize your home.

Kill it. Kill it with fire!

Generally speaking, you don’t actually kill head lice with fire. Not that it wouldn’t work, mind. But they’re living on your skin, so you don’t really want to apply fire. Instead, you apply neurotoxins.

Yes.  Neurotoxins.

The most common over-the-counter medicines for head lice are pyrethrins, which kill by “targeting the nervous systems of insects”. Specifically, “pyrethrins delay the closure of voltage-gated sodium ion channels in the nerve cells of insects, resulting in repeated and extended nerve firings. This hyperexcitation causes the death of the insect due to loss of motor coordination and paralysis.” So, yes. You’re consigning the little bugs to a slow and agonizing death. But it also functions as an insect repellent, driving survivors from the treated area – sort of the over-the-counter version of displaying your enemies’ heads on pike, I guess.

Note that pyrethrins can affect humans, in sufficient doses. The EPA recommends different daily oral exposure limits for pyrethroids of anywhere from 0.005 to 0.05 mg per kg per day (depending on the specific pyrethroid), and OSHA has set an occupational exposure limit for a standard work day of 5 mg per cubic meter. Note, however, that most lice treatment shampoos run around 0.33% pyrethrins by weight. What does that mean?

well, I weigh 133.35 kg, meaning that my safe limit for daily oral exposure to pyrethroids ranges from 0.66675 mg to 6.6675 mg per day, depending on the specific pyrethroid. Assuming the specific pyrethroid in the medicine is the one in the 0.005 mg per kg limit, I could drink 202 mg of the medicine and generally be all right. (Note: do not do this!) That’s not a whole lot, though, which is why these medications fall under the category of “safe when used as directed“.

Head lice medication cocktails are not a use as directed.