context: â A kiss is still a kiss,â the old song goes. But a kiss can also make you sick. Germs that live in saliva spread easily through kissing. The infections they cause -- surprise, surprise -- are common among teenagers. Your teen can try to protect himself by avoiding kissing if he suspects someone is sick. But never kissing is pretty impractical. If you know the early signs of infection, however, you can head off some of the worst symptoms. Infectious mononucleosis is caused by Epstein- Barr virus, which can be found in saliva. Mono shows up most often between the ages of 10 and 19. What mono feels like: It's easy to mistake mono for the flu at first. Symptoms include fever, sore throat, body aches, fatigue, and swollen lymph nodes. If you have flu symptoms that don't seem to be going away, talk to your doctor. What you can do: There's no vaccine for mono and no specific medication to treat the infection. But there's plenty your teen can do to feel better. Take acetaminophen ( Tylenol) or ibuprofen ( Advil, Motrin) to relieve achiness and to lower fever. If the throat is sore, try gargling with salt water or using throat lozenges. Get plenty of rest and drink lots of fluids. What to expect: Mono usually goes away on its own in two to four weeks. But in some cases, the symptoms may linger for several months or longer. Cold sores are painful blisters on the mouth, lips, or nose. The culprit is herpes simplex virus, which spreads through kissing or close contact. There is no cure once a person has contracted the virus. What cold sores feel like: Your teen may notice a tingling or burning sensation at first. Then a painful, fluid-filled blister forms. Cold sores can be very raw-looking and take several days to a week to heal. What to do: To prevent cold sores, avoid contact with people who have sores on their lips or mouths. Once you've had a cold sore, you're likely to get them again. Several medicated creams, including both over-the-counter and prescription brands, can speed healing when you have a cold sore. The catch is that you have to apply them as soon as possible after symptoms appear. If you've already had one cold sore, it's wise to keep a medicated cream handy. If your teen keeps getting cold sores, talk to your doctor. An antiviral medication in liquid or pill form is also available by prescription for serious infections. If your teen has symptoms of a cold sore, tell him to avoid kissing people to prevent spreading the virus. Don't share drinking glasses, spoons and forks, toothbrushes, or other items that can spread it. What to expect: Cold sores go away on their own. But because the virus can hang out in nerve cells, they may come back. Luckily, they tend to get less severe over time. Strep throat is an especially painful form of a sore throat, caused by a highly contagious form of bacteria. Strep throat infections are most common between the ages of 5 and 18. Although strep throat is most frequent between late fall and early spring, your teen can get it at any time of year. What strep throat feels like: Strep throat feels like a really bad sore throat. Your teen may notice that her tonsils are inflamed. She may also see yellow or white patches at the back of her throat. Strep often causes a fever. What to do: If you think your teen may have strep, call your doctor. Strep throat needs to be treated with antibiotics. Otherwise, it can lead to serious problems. Gargling with salt water or sucking on throat lozenges will help ease the pain. Acetaminophen or ibuprofen will reduce a fever. What to expect: With antibiotic treatment, strep throat can last as long as a week or two. Untreated, strep throat can lead to more serious infections such as rheumatic fever or kidney disease. That's why it's so important to see your doctor if your teen has a severe sore throat. Your teen can get these common fungal infections by exposure to damp areas like locker rooms and swimming pools, or in the case of athlete's foot, by sharing shoes with someone who has it. What they feel like: Athlete's foot causes itchy, cracking sores between the toes and sometimes on the soles of the feet. Jock itch causes similar itchy, cracking sores in the groin. The sores may weep and smell nasty. Athlete's foot can also cause redness on the bottom and sides of the foot. This form is called moccasin athlete's foot. What to do: Use an over-the-counter antifungal cream, spray, or powder to get rid of athlete's foot or jock itch. If that's not enough to get rid of the symptoms, talk to your doctor about prescription-strength medication. To prevent getting athlete's foot or jock itch again, tell your teen to wash and carefully dry his feet and groin area after showering. Change socks and underwear every day. Alternate wearing different pairs of shoes to allow the insides to fully dry out. Dust the insides of socks and shoes with medicated foot powder. What to expect: Your teen's symptoms are likely to get better within a week or two. With careful hygiene, he can avoid getting athlete's foot or jock itch again.