People with light skin and eyes are more likely to have freckles because they have less melanin, a chemical in the skin that protects it from sun damage by reflecting and absorbing ultraviolet (UV) rays. Instead of tanning, they freckle.
Some people’s freckles fade away almost completely in the winter, and then return in the summer, when the person is more likely to sunburn. Sunscreen can help protect everyone (freckled or not) from the Sun’s harmful rays.
Scientists do not know exactly why people need sleep, but studies show that sleep is necessary for survival. Sleep appears to be necessary for the nervous system to work properly. While too little sleep one night may leave us feeling drowsy and unable to concentrate the next day, a long period of too little sleep leads to poor memory and physical performance.
Hallucinations (seeing things that aren’t really there), vision problems, and mood swings may develop if sleep deprivation continues.
Babies grow in their mother’s uterus, a special organ that houses the baby until it is born. At the start of pregnancy, a mother’s egg is fertilized, which makes a new cell. The cell divides quickly into many more cells. At about one week, this tiny mass, called an embryo, sticks to the wall of the uterus, and begins to grow. From the moment of conception, 46 chromosomes and tens of thousands of genes combine to determine a baby’s physical characteristics—the sex, facial features, body type, and color of hair, eyes, and skin. At the eighth week, the embryo is called a fetus.
By the end of the twelfth week, the fetus is completely formed and is able to make a fist, can turn his or her head, and can squint and frown. Until the baby is ready to come out, it grows inside its mother’s uterus. When the baby is ready to be born, at about 40 weeks, the mother starts to feel labor contractions. The uterus squeezes and pushes the baby out of the uterus and into the world.
Germs are everywhere! Most germs spread through the air, invading our homes, pets, and family, and sometimes they make us sick. Besides your bathroom toilet and the kitchen sink, everyday items like shopping-carts, restaurant menus, computer keyboards, and the shower curtain contain germs. These items contain bacteria, mold, and rhinoviruses (instigators of the common cold) that can lead to sickness. In fact, cold and flu viruses can survive for 18 hours on hard surfaces.
Common household items can be swabbed with a disinfectant wipe easily before use in order to prevent germs from spreading. Washing your hands with soap and water, using a hand sanitizer, and avoiding touching your face with your hands after using these items also helps keep germs away from you. To eliminate dust mites—those little critters that live in your bed sheets and feed on dead skin cells—don’t make your bed for a while. Studies have found that dust mites need humidity levels above 50 percent to survive and cannot live in the arid conditions of an unmade bed.
The word “smog” was first used in London during the early 1900s to describe the combination of smoke and fog. Today, the term “smog” is used to describe a mixture of pollutants, primarily made up of ground-level ozone. Ozone can be beneficial or harmful depending on its location. The ozone located high above the surface in the stratosphere protects human health and the environment, but ground-level ozone is responsible for the choking, coughing, and stinging eyes associated with smog.
Smog-forming pollutants come from many sources, such as automobile exhaust, power plants, factories, and many consumer products, including paints, hair spray, charcoal starter fluid, solvents, and even plastic popcorn packaging. In many American cities, at least half of the pollutants come from cars, buses, trucks, and boats. Scientists estimate that about 90 million Americans live in areas with ozone levels above the standards for health safety.
Yes and no. Bones are hard connective tissue, made up of bone cells, fat cells, and blood vessels, as well as nonliving materials, including water and minerals. Some bones have a very hard, heavy outer layer made out of compact bone. Under this layer is a lighter layer called spongy bone, which is located inside the end, or head, of a long bone.
Spongy bone is tough and hard, but light, because it has lots of irregularly-shaped sheets and spikes of bone (called trabeculae) that make it porous (full of tiny holes). The soft, jelly-like inner core of bone is called the bone marrow. It is where red blood cells, certain white blood cells, and blood platelets are formed. The jawbone is the hardest bone in your body. Although bones are hard, they are not the hardest substance in the human body: the enamel on your teeth is harder.
Technically, no. While it is responsible for receiving and transmitting all messages of pain for the whole body, the brain itself does not have pain receptors.
That means that, if you could somehow gain access to another person’s brain, you could poke it or pinch it and that person would not feel the pain.
If you want to look clean and smell nice, your clothes need to be washed frequently. Most clothing is made of tiny threads that are woven together. As you go about your day, dirt and odors get trapped in the weave of your clothes and can only be removed by washing.
Clothes must be jiggled and swished around quite a bit in water—as is done in a washing machine—to best remove dirt and odors. Detergent is added to the water to help the process: it can break up oily particles into smaller pieces that can be whisked away, and it can surround other dirt particles and pull them away from fabric.
Itchy, red skin may be the sign of athlete’s foot, a skin infection caused by a moldlike fungus. The fungus needs a warm, moist environment to live and often grows on the floors of locker rooms and public showers and in swimming pools and whirlpools. It also loves stinky old tennis shoes. When a foot comes in contact with the fungus, it becomes red and itchy. Sometimes, moist, white, scaly lesions or sores develop between the toes and spread to the soles of the feet.
In boys, sometimes athlete’s foot fungus spreads to the groin area, where it is called “jock itch.” The fungus sometimes spreads from one location to another as it is picked up on a bath towel, and the groin area, which is warm and moist, helps the fungus flourish.
The inability to hear, or deafness, can occur for many reasons. Some types of hearing loss result from something blocking sound as it travels from the outer ear to the eardrum and the tiny bones in the middle ear. Other types of loss arise from damage to or a defect of the inner ear or the auditory nerve, which is the nerve that carries sound signals from the inner ear to the brain. Deafness can happen as a result of disease, including severe ear infections, or it can be inherited, with the deafness being apparent at birth or sometimes showing up years later. Injuries and accidents also account for many cases of deafness.
Extremely loud noises, like those that come from an explosion, can cause deafness, though that loss of hearing is sometimes temporary. People who work in noisy factories or those who are frequently exposed to very loud music can also develop hearing loss over time. Many people gradually lose some or all of their hearing when they reach old age, but some of those types of hearing loss can be overcome by wearing a hearing aid, which makes noises like speech or music louder.