Valentine's Day may be worst day to kiss MAYWOOD, Ill., Feb. 1 (UPI) -- Valentine's Day falls smack dab in the middle of flu and cold season, so kissing may not be such a good idea, a U.S. infectious disease expert suggests. Dr. Jorge Parada, medical director, infectious disease at Loyola University Health System in Maywood, Ill., said changing weather or temperatures are often blamed for winter's coughs and sniffles, but in reality, colds, coughs and the flu are infectious diseases "caught" from one human to another. "Becoming too hot or too cold can cause stress to the body, weaken the defense in fighting off infections and thus make us more vulnerable," Parada, who is also a professor of preventive medicine at Stritch School of Medicine, said in a statement. But a person has to be exposed to a virus or bacteria to catch it. "Mid-February can be the peak season for infectious diseases, such as the seasonal and H1N1 flu, mononucleosis, colds and coughs," Parada said. And don't rely on obvious signs of illness -- such as sneezing or fever as a tip off. People with infectious diseases start shedding the virus before they experience the full effect of the illness. In fact, drinking from the same wine glass or sharing dessert with the same fork may seem romantic, but it also may lead to infections. "Someone can have a cold sore that hasn't erupted yet and use lip balm which is then shared, and the cold sore virus -- herpes -- is transmitted," Parada said. A shared pillowcase, napkin or towel can also actually be a conduit for disease, especially if someone has a sore or cut. Parada said it takes 10-14 days for the flu shot to have full preventive effect, so there is still time to get one and have it working before Valentine's Day.