Karen Hill

Idiopathic scoliosis, a sideways curve of the spine of unknown cause in adolescence, is now believed to require active treatment in only about 10 percent of cases. When treatment is called for, a cast or a device called a Milwaukee brace is widely used. At least 60 percent to perhaps 80 percent of the cases … Read more

Morning sleepiness in teenagers (or in anyone else) may have a cause as simple as lack of sleep, perhaps because of too much homework after a part-time job, followed by television. In that case the cure may be to sleep more, cut down on some sleep-robbing activities, and gradually change bedtime and waking time in … Read more

The description fits what doctors still call growing pains, or benign limb pains of childhood. The suffering is real, though the source is still not understood. Most pediatricians do not believe growing pains are actually related to the child’s growth. For one thing, the location is ill defined, not specifically at the limbs’ growth plates, … Read more

Experts suspect that the problem is not that tired parents are using strollers while shopping, but rather that they may be preventing their children from moving enough the rest of the time. Child development specialists think that freely crawling, cruising, and toddling are a normal progression in a child’s physical and cognitive development. But as … Read more

There is no definitive answer, but its structure suggests a key role in the strong grip for hanging and power grasping. The middle finger’s length is one aspect of hand evolution that people have in common with apes. For many primates, the middle finger is the functional axis of the hand and the longest finger. … Read more

Your adult height will probably be somewhere in between. Some rough estimates can be made based on the growth patterns of many children. These methods assume that there is no disease or hormonal problem to hinder your genetic potential. Because height at the age of 3 is about 60 percent of adult height for girls … Read more

Slightly more than half of all twins born are male. In conjoined or Siamese twins, the picture is complicated both by their extreme rarity and by their very low overall survival rate, which is variously given at 5 percent to 25 percent. Conjoined twins are always identical, because they always come from a single fertilized … Read more

The advantages for girls begin even before birth, and like so many other differences between the sexes may be tied to hormones. For example, significantly more male fetuses are spontaneously aborted or stillborn. The reasons need more investigation, but they seem to include sex differences in chromosomal structures and possibly a slower maturing of boys’ … Read more

Many studies have found a relationship between birth order and birth weight, with the later-born children in a family tending to be larger, and birth weight has some correlation with eventual height. For example, a 1988 study at the Children’s Hospital of the University of Kiel, Germany, investigated adult height in families with three or … Read more

In fact, each year more males are born than females. The normal slight excess of male births is usually attributed to the slightly greater motility of sperm carrying the male, or Y, chromosome. It was recently discovered that in the average ejaculation, there are slightly more sperm carrying the X chromosome, necessary for conception of … Read more

Fetal urine is the main component of the amniotic fluid that bathes the developing fetus. It is excreted into the fetal sac inside the womb as the fetus develops. Normally, the fetus “breathes” this fluid into its lungs, and it is essential for the normal development of the lungs. The fluid contains some fetal cells, … Read more

Most gulls do not have feet that are adapted to perching in trees and clinging to tree branches. Most have slightly webbed feet that help them move about in the water, so when they are on land, they do better walking on rocks or soft surfaces like sand. Pure probability also puts gulls on the … Read more

Evolutionary biologists have suggested that morning sickness is a mechanism to help women avoid noxious substances that might harm the fetus at an early stage of development. Formerly, scientists had assumed that the sickness early in pregnancy was related to a sharp rise in the hormone estrogen. But as some scientists point out, the sickness … Read more

Woodpeckers like the acorn woodpecker of California, which hits the wood with its bill at speeds of 12 to 15 miles an hour, manage to keep their wits because their brains are held firmly in a case, which acts as a shock absorber. The bird’s body also moves in a single plane like a metronome, … Read more

Bird droppings combine the whitish waste products processed by the liver and kidneys with the darker wastes that come from the digestive tract. In birds, the nitrogen-rich wastes are turned into a white-colored paste that is composed mostly of urates. The urates often form a separate white blob, as anyone who has worn a new … Read more

There are three kinds of evidence. First, there is epidemiological data from studies of AIDS outbreaks. For example, in sub-Saharan Africa, where mosquitoes are extremely plentiful, the very people who would get bitten most, young children who are outside playing, comprise the one group that is not HIV-infected. The AIDS epidemic is among the sexually … Read more

ARDS, which stands for acute respiratory distress syndrome, or sometimes adult respiratory distress syndrome (to distinguish it from a lung problem in newborns), is not a disease itself, but a type of severe acute lung dysfunction that can result from disease or injury, according to the ARDS Support Center, a clearinghouse for information. The condition … Read more

Foot-and-mouth disease is a danger only to animals, not to humans, and the chance of getting mad cow disease from dairy products is zero to almost zero. The risk is so slight that there is an exemption allowing the importation of milk from countries where mad cow disease has been found. Transmissible spongiform encephalopathy, or … Read more

Cat scratch fever or cat scratch disease is a mild flu-like infection, usually causing swollen lymph nodes and a low-grade fever, that was first described in the 1950s as being associated with cat scratches, especially from kittens. The infection usually goes away by itself in a few weeks and can be treated with antibiotics, but … Read more

Try a longer vacation. Altitude sickness is not linked to a person’s general condition but to specific adaptations to high altitudes; even puny permanent residents are usually immune. Medical experts say the body usually adjusts within a few days to the complex changes in blood chemistry that come about because of the relative shortage of … Read more

From the human point of view, some viruses can be useful, potentially useful, or at least interesting. Under the “interesting” heading would fall the mosaic virus, which produced the fantastically variegated tulips of the tulipomania investing craze in seventeenth-century Holland. The rare infected bulbs were treated almost like a currency with a constantly multiplying value … Read more

It is not cold feet and wet heads that are the problem, infectious disease experts say, but the fact that human beings are warmth-loving social animals. At least in cold climates, widespread outbreaks of diseases like colds and influenza tend to start in winter months, when people spend more time together indoors in close quarters … Read more

Immunity is long-lasting because some of the many kinds of cells that make up the normal human immune system are naturally able to retain a “memory” of the defense efforts aroused by certain infections or vaccines. There are many kinds of immune cells, including T cells and different types of white cells. Their interaction with … Read more

There is no simple answer, but in general, this is very unlikely. In theory such reinfection is conceivable, but there are no documented cases of it. The possibility would depend on the organism and how the person’s immune system responded to it. If a pathogen is on the skin a long time, the person has … Read more

Polite East Asian people with a cold may wear a mask with the aim of preventing its spread; this is especially common in Japan. In China, the idea may be to cut down infection or it may be a reaction to high levels of visible pollution; in some of China’s industrial areas, masks are worn … Read more

There are no guarantees, but there are some ways to cut your risks. The most important are avoiding crowds, especially during the peak cold seasons of September, late January, and April; avoiding people who obviously have colds; avoiding shaking hands with people who might have them; avoiding rubbing the nose and eyes; and washing your … Read more

They are referring to how the germs react to one of the basic tests in bacteriology, the Gram stain or Gram’s stain, which distinguishes between two major classes of bacteria by how they take up certain dyes. On a microscope slide, heat-treated gram-positive bacteria take up a purple dye (originally gentian violet), which is then … Read more

There are viruses that infect disease-causing bacteria, as well as many other bacteria. Called bacteriophages, meaning bacteria eaters, they were discovered during World War I and named in 1917. Much smaller than the bacteria they attack, bacteriophages cannot grow and multiply on their own. Instead, like other viruses, they attach themselves to the surface of … Read more

There are three likely explanations, based on recent research. First, what do you eat and drink? A lunch high in carbohydrates, especially if no protein is eaten along with bread and milk, is likely to produce calm to the point of sleepiness, because of the complex role of carbohydrates in shifting the balance of neurotransmitters … Read more

Some disease-causing organisms, or pathogens, can thrive and multiply for some time on an object like a phone receiver spattered by the saliva of an infected person. But most bacteria and viruses quickly die when moisture disappears, usually after one or two hours for the saliva spray. Different pathogens have different survival times, ranging from … Read more

There is both concern and controversy over mercury in fish, but an occasional tuna fish sandwich for an adult who is not going to become pregnant is not the main worry. The biggest concern is the risk to a fetus. Mercury builds up in muscle cells of fish and in those who ingest it, and … Read more

Kaolin, also called China clay, is a chalky rock composed chiefly of kaolinite, together with quartz and mica. It is formed by the weathering of aluminum-rich silicate rocks, especially feldspar. Over the ages, the crystals wash into large sedimentary deposits. Purified kaolin in a suspension with pectin from apples has long been used to fight … Read more

Milk thistle does contain chemicals called flavones that appear to benefit the liver, but these compounds are not very soluble in water, and the tea has only about one-tenth the strength of the original plant material. In fact, the chemicals are poorly absorbed through the gastrointestinal tract and would probably be medically effective only if … Read more

Calcium citrate, the type found in calcium-enriched orange juice, is less likely to cause stomach upset than other forms. Calcium carbonate and calcium gluconate are the two forms that are most common in supplements; they both tend to be adequately absorbed. Calcium citrate is a good alternative, because it is very well absorbed and also … Read more

The assumptions of the question are not totally true. It’s not just drinking, but where you drink and what kind of clothes you have on that determine whether the body ends up warmer or colder. What happens is that alcohol causes the blood vessels in the skin to dilate, so that more blood passes through, … Read more

The Physicians’ Desk Reference for Nonprescription Drugs (PDR) does not advise against taking normal doses of aspirin in addition to acidic foods or alcohol, itself a powerful drug, but there may be deleterious interactions for some people. That is because aspirin is an acid, acetylsalicylic acid, and when aspirin is taken with acidic foods and … Read more

Caffeine is not a direct stimulant; instead, it blocks the action of another chemical, naturally present in the human body, that has a calming effect on the activity of cells, especially those in the brain and spinal cord. Caffeine, found in tea, coffee, and cocoa, is one of a class of chemicals called methybcanthines that … Read more

Quinoa is a significant source of calcium, but you would have to eat a large amount of it to get a full daily supply. The National Academy of Sciences recommends 1,000 milligrams of calcium a day for most people, more for those over 50, and according to the United States Department of Agriculture, a cup … Read more

They are usually talking about six to eight glasses of 8 ounces each, for a total of 64 ounces a day. It does not hurt to drink more, especially if you are exerting yourself. You might weigh yourself before and after a workout and drink 16 ounces of water for every pound you lose. With … Read more

Not any more than eating enough of any other protein. If someone is severely protein deficient, high quality protein like that in gelatin might make a difference, but the average person gets plenty of protein. It’s the same with calcium. It would help your nails if you were totally deficient, but if your bones are … Read more

Repeated studies have failed to find any link between eating chocolate (or anything else) and teenage breakouts. As long ago as 1950, a study by a dermatologist compared the results of giving teenagers with acne candy bars that just tasted like chocolate and those made with real chocolate. Photographs showed no difference in new breakouts. … Read more

The short answer is that aflatoxin is of very little concern. Aflatoxin is produced by the fungus Aspergillus flavus, and most people don’t eat moldy food, because it tastes bad. Documented human aflatoxin problems usually occur in tropical countries, where the wet climate is conducive to mold growth, or in extremely poor ones, where people … Read more

It can be either very healthful or very noxious, or both. A study by scientists at the U.S. Department of Agriculture, done with money from the Peanut Institute, suggests that peanuts may contain enough resveratrol, the compound in red wine associated with a low rate of heart disease, to be helpful to human health. The … Read more

Yes, if it is a real cheese pizza with real tomato sauce. For a complete diet, first you need to consume a sufficient quantity of food to get enough calories. Then you need a good source of protein and a supply of certain essential nutrients, like vitamins B12 and C, found only in certain kinds … Read more

The most likely culprits for yellow clothing stains are body secretions called apocrine sweat and sebum, the oily secretion of the sebaceous glands. Deodorants and antiperspirants may also play a role. The sebaceous glands are usually associated with hair follicles. Cells filled with fatty droplets die and burst, providing lubrication for the skin and hair. … Read more

Perfect pitch, which is also called absolute pitch, is the ability to name any note (such as A, B flat, C sharp) just from hearing the tone, without reference to other notes in a scale. Relative pitch, which is far more common, is the ability to tell what note is being played by judging the … Read more

You can certainly be cursed at, by archaeologists. The history of ancient Egypt, for example, is full of holes left by grave robbers, and remaining tombs are at risk from tourism and development. Egyptians believed tomb inscriptions could confer either blessings or curses on visitors, and early visitors probably believed so, too. Tomb builders wanted … Read more

Medieval theologian-philosophers tried to calculate that incalculable number based on the notion that angels were the smallest possible physical creatures, though with very large spiritual powers. Based on that same definition of size, a modern physicist actually made a calculation for an even smaller dance floor: the number of hypothetical angels that could dance on … Read more

There are some rules of thumb for estimates for a limited area, but estimates for whole countries or the world are just guesstimates. Archaeologists tend to find and count all the formerly inhabited sites in a study area; make an educated guess about which ones were occupied at a certain period, usually based on pottery … Read more

Historians of science find the obvious explanation for the base-10 system at the fingertips of human beings, all ten of them. Not so coincidentally, the word digit comes from digital, the Latin word for finger or toe. Counting on the fingers (base 10) or the fingers and toes (base 20) is the apparent root of … Read more

The long pointed bottom of the typical amphora actually gave it an excellent shape for stacking against a ship’s hull, ensuring that the oil or wine within would be safe during transport. In the evolution of amphorae, they often began rounded and egg-shaped and shifted to pointed, because the long bottom of the brittle pottery … Read more

Not unless the victim that is, patient chanced to be suffering from a hypertension crisis or an abnormal buildup of iron in addition to whatever disease the doctor thought he was treating. For example, draining 10 to 12 ounces of blood, for a start, and up to 80 ounces in all, was routinely prescribed during … Read more

There is no scientific evidence that any person ever spontaneously combusted, and no scientifically known means by which it could happen. In a typical case where there has been a report of a body burning unusually, a simple or at least plausible explanation is available when the case is examined in detail. A statistically typical … Read more

Historians agree Greek fire existed, but debate its nature. Some credit Callinicus of Heliopolis with building fire-spouting ships that defended Constantinople from the Arabs in 673. Greek fire was described as a liquid that burned even on the sea surface, with smoke and whooshing sounds. Candidates for ingredients include petroleum, resin, and quicklime, plus an … Read more

The building does move, but the motion is a very slight bending, only about a quarter of an inch, in winds of more than 75 miles an hour. The illusion of a larger motion probably has to do with wind-whipped clouds; an observer on the ground can see a tall building appear to “fall” if … Read more

Historically speaking, New York City is less prone to thunderstorms than many areas of the country, but the island of Manhattan is not immune to lightning. For example, the Empire State Building is struck by lightning on average about two dozen times a year. The good news for Manhattanites is that modern high-rise buildings have … Read more

Just about any organic material will explode if it is fine enough, dry enough, in suspension in air, and confined. All it takes is the fuel, oxygen, and a spark. Sugar, coal dust, wood dust, walnut hulls, the ingredients of children’s modeling dough, and some medications have also been involved in recent dust explosions. Organic … Read more

They work somewhat the way an old-fashioned stereopticon viewer (holding two slightly different photos) works. Each eye focuses on a separate image, but the brain combines them into one image that gives the illusion of depth (the third dimension) in addition to width and height. It does this by matching up the similarities and adding … Read more

Several kinds of technology have been used for touch screens. If the screen responds without actually being touched, it probably uses a system that has tiny infrared light emitters and detectors along the edge of the screen. When a finger interrupts the grid of beams, a computer can tell its exact position. Some screens sensitive … Read more

The paper is oxidizing, one of several destructive processes that affect paper. Newsprint is high in lignin, one of the main structural components of wood. When lignin is in contact with oxygen, a highly reactive chemical, the reaction changes the way the fibers reflect light, discoloring the paper. Oxidation also produces more acid, a major … Read more

Antifogging agents are chemicals that force the tiny droplets of water that make up fog to merge into a transparent sheet. An agent is sprayed as liquid on the lens, and when it dries, it forms a clear film. Normally, water beads up, but with the film, the beads run together. The water is still … Read more

There are two reasons why cookware may heat up excessively in a microwave oven. The first is the same effect that occurs in cooking: friction. Microwaves are rapidly fluctuating electromagnetic fields, which push on electric charges and twist naturally polarized particles like water molecules back and forth. In liquid water, this twisting leads to molecular … Read more

The “steam” you see is what steam engine enthusiasts call wet steam, because it contains unevaporated water as a mist within the actual water vapor, which is a colorless, odorless gas. Dry steam does not contain any unevaporated water. Steam vapor forms at temperatures above the boiling point, normally 212 degrees Fahrenheit. Visible steam is … Read more

Conditions that are very like an allergy to winter are not only possible but common. Your friend’s problem could be an asthmatic reaction to exercising in the cold, or it could be an allergy to something she is exposed to in winter even more than in the traditional allergy season. It could even be that … Read more

Probably not, but more research is needed to know the degree of danger presented by the fumes emitted from diesel vehicles. Cars, trucks, and buses, especially diesel buses, emit large amounts of tiny particles that remain airborne for long periods. Because they linger, holding the breath until the bus passes is ineffective in keeping them … Read more

There are many theories about the high AIDS rates, especially in sub-Saharan Africa, and answers almost certainly lie in combined economic, sociological, political, and medical factors. For example, the rate of HIV infection in Botswana, the highest in the world at 35.8 percent of adults, has been linked to Botswana’s location and excellent road system, … Read more

Scientists don’t know for sure, but the most likely explanation is that rats probably would not survive an encounter with an infected carnivore, and so would not be around to transmit the disease to people. It is also possible that rats may lack a means of transmitting the virus within the species, because of mouth … Read more

From 1930 to 1937, the United States suffered its worst drought in history. Across 50 million acres (20.25 million hectares) of land in Kansas, Oklahoma, Texas, New Mexico, Colorado, Nebraska, and the Dakotas, dry weather and winds caused massive dust storms that carried particles as far as New York City. In 1933 and 1934, the … Read more