Ask Doctor Cory.

How does hair grow?

Laura Burns

Marseilles, Illinois

Why do people lose hair and get bald?

Kenyada Himes

San Antonio, Texas

Dear Laura and Kenyada:

Just like with skin cells, we regularly shed hairs and grow new ones to replace the old ones. We usually lose about 50 to 100 hairs a day. Each hair grows for two to six years, then rests. At any one time, 15 percent of your hair is resting while 85 percent of your hair is growing. After a short resting phase, the hair falls out and a new one begins to grow. Hair usually grows about half an inch a month and faster in the warm seasons. A regular head of hair has about 100,000 hairs on it.

Heredity, hormones, and aging all play a part in the development of male-pattern baldness. A change in the male hormone, testosterone, is linked to baldness in that it somehow keeps lost hair from being replaced with regular hair. Instead, lost hair is replaced by very short, very fine hair that you can hardly see.

There are also some nutritional or medical conditions, such as alopecia areata, that cause hair to thin or fall out. Hair loss in young girls is sometimes due to hairstyles where the hair has been braided or pulled too tightly.

Dear Dr. Cory,

How do you get pinkeye? Why does it feel like you just want to rub and rub?

Renee Shumake

Jefferson, Georgia

Dear Renee:

Pinkeye, or conjunctivitis, can be caused by a bacterial or viral infection. Sometimes it can be due to an allergy.

Pinkeye caused by a virus or bacteria is easily spread from one person to another. For this reason, people with this type of pinkeye usually need to stay home, wash their hands often, and not share towels, washcloths, sheets, or pillows. In fact, items that the infected person has used should be washed to keep the infection from spreading to other family members.

Pinkeye from allergies is caused by coming in contact with a substance to which you are sensitive (allergen). It can cause intense itching. Your body reacts to the allergen by releasing a chemical called histamine. Histamine causes blood vessels to enlarge; it also irritates nerve endings in the skin, which makes you itch.

If you ever have pinkeye, it is important to tell your doctor what kinds of symptoms you have (such as swelling, itching, redness, pus, pain) so that he'll know whether he needs to see you and what kind of medicine you'll need. If the pinkeye is caused by a bacterial infection, he'll probably prescribe antibiotic drops or ointment. If it is pinkeye due to allergies, it may be possible to prevent by avoiding the allergen. Drops can be prescribed to help with the itching. Putting cool compresses on the eyes, made from clean washcloths rinsed in cool water, can also be soothing to a person with allergic conjunctivitis, according to Dr. Shailaja Valluri, an Indianapolis eye doctor.

Dear Dr. Cory,

At my school, 1000 Oaks, we had a day called a "Field Day." I ran an 800-meter race. After I ran the race, I could hardly breathe, walk, talk, or even just stand. Do you know why all that happened?

Sara Polk

San Antonio, Texas

Dear Sara:

We are not surprised that you would feel this way after running 800 meters, especially if you are not used to running. You get tired because your lungs, heart, and muscles are probably out of shape. When you exercise regularly, your muscles are able to take oxygen from the blood more easily, making you less tired. People who run regularly increase their cardiovascular strength gradually. If you expect to run such a distance and not be out of breath, you're going to have to build your cardiovascular strength, too.

Start out slow. You should be able to carry on a conversation while you are jogging. If you are out of breath, it generally means that you have started too fast. Slow down or walk until you catch your breath. Try jogging twice around a track once or twice a week until it gets easier. Then you can gradually increase your speed and your distance.

Be sure to do warm-up exercises to help avoid injuries and soreness the next day, and to cool down after you run. Drink plenty of fluids each day, especially in hot weather. You might try running with a friend to make it more fun.

You may also want to get a copy of the book Improve Your Running Skills. Part of the Usborne Superskill paperback series, this book is a complete guide on how to be a successful runner.