Wash your hands before you eat, cover your mouth when you sneeze, opt for the fist-bump over the handshake…you know all the ways to protect yourself from commonly contagious sickness. But there are some conditions that antibacterial soap or a tissue can’t protect you from. Here, 4 things you never knew you could catch:

Cavities
You can floss, brush, and avoid sweets all you want, but if your mate doesn’t follow the same routine, you could fall victim to his or her poor dental hygiene. Researchers from the University of Helsinki, in Finland, found that oral bacteria that cause periodontis, gingivitis, and dental caries (aka cavities) can be passed between adults living in close contact with each other. Ick. The study, published in the journal Oral Microbiology and Immunology, followed 20 married couples, ages 37 to 70 years old, who had been married for at least 10 years. In four of the couples, both members had bacteria associated with periodontis and gingivitis. Three of those couples also harbored mutans streptococci bacteria (the main cause of cavities). Researchers found that the specific DNA of the bacteria was similar between members of a couple, yet different between unrelated subjects, suggesting transmission of the oral bacteria between spouses.

Cancer

HPV is a contagious virus that can increase your risk for certain cancers.

No, you cannot catch cancer from someone suffering from the disease—but you can catch the human papilloma virus (HPV), seriously increasing your risk of developing cancers of the cervix, penis, anus, mouth, and throat. According to research from Duke University, more than 6 million people in the US become infected with HPV each year (the disease spreads through sexual contact with an infected person). And while most people can clear the infection on their own within 1 to 2 years with little or no symptoms, the infection persists in some people—and the longer the infection persists, the more likely it is to lead to cancer.
Autoimmune Disease

Autoimmune diseases may be transmisseable between close relatives.

As if living with celiac disease isn’t miserable enough, those battling the gluten allergy may need to worry about exposing their loved ones. According to research published in the journal Clinical Gastroenterology and Hepatology, first-degree relatives and spouses of those with celiac disease are at an increased risk of developing nonceliac autoimmune disease, like Crohn’s disease, psoriasis, rheumatoid arthritis, lupus, or ulcerative colitis. Researchers found that over a 10-year period, 4.3% of celiac relatives and spouses developed nonceliac autoimmune disease, compared with 3.3% of relatives of control subjects (those without celiac disease). Researchers speculate that the susceptibility is a result of sharing gut bacteria. (Learn how to hack your gut bacteria for faster-than-ever weight loss with the Good Gut Diet.)

Obesity
Call it infectobesity: Turkish researchers recently discovered a virus in the adipose tissue (body fat) of obese adults: human adenovirus-36 (Ad-36). People exposed to Ad-36 are 300 times more likely to be obese than those who haven’t been exposed. Worldwide, more than 15,000 people in nine different countries have been tested for antibodies to the virus (usually the body fights off the virus, but the damage is already done), and with remarkable consistency, people who are obese are far more likely to show signs of infection.