A new year is a time for a fresh start, so let’s start by putting to rest certain medical myths and stereotypes. Some of them are simply silly, while others are harmful.

Myth: Shaving makes hair grow back quicker and thicker

Most of us heard this myth for the first time in middle school, and there are adults who still believe it. But no, shaving does not affect how your hair grows. There are many reasons this myth became popular. For starters, young people start shaving around puberty, when their hair is naturally going to start coming in thicker and growing more rapidly. Additionally, Scientific American explains, a shorn hair may appear thicker or darker because its shaft is revealed, as opposed to its tapered end. “Those short hairs, sticking straight up from their follicles, may even appear coarser,” the magazine says. However, “the tapered hair you had is the hair you’ll get back.”

Amy McMichael, chair of the Department of Dermatology at Wake Forest Baptist Health, drives home the idea. She told Scientific American, “Women shave their legs all the time. They would be like gorillas if the hair was coming back thicker or darker. Plus we would never have to think about hair loss on our heads if cutting the hair shaft would make it come back thicker.”

Read: Does A Blood Transfusion Change Your DNA?

Myth: People with diabetes got it from eating too much sugar

Obesity is a risk factor for diabetes and research has shown a link between sugary drinks and the disease, in which the body doesn’t produce enough of the hormone insulin or does not use it properly, leaving high sugar levels in the blood. However, the American Diabetes Association says genetics and family history, ethnicity, and age all play a role in whether someone will develop diabetes. “Most overweight people never develop type 2 diabetes, and many people with type 2 diabetes are at a normal weight or only moderately overweight,” the group notes. The exact mechanisms that cause diabetes are not entirely understood. With type 1 diabetes, it is “caused by genetics and unknown factors that trigger the onset of the disease,” while type 2 is believed to be a combination of genetics and lifestyle.

Myth: Childhood vaccines cause autism

No matter what the British medical journal The Lancet does in the future, it will always be tied to the source of this pervasive myth. In 1998 it published a report that claimed the vaccine against measles, mumps and rubella caused autism spectrum disorder, a group of developmental disorders varying in severity and associated primarily with trouble communicating and interacting with other people. That report was later completely debunked and was retracted. However, people still believe that vaccines, both the MMR and others, somehow cause autism. Scientists still don’t know exactly what causes autism, but they know what it’s not: the Centers for Disease Control and Prevention has reiterated “studies have shown that there is no link between receiving vaccines and developing ASD.”

This myth is particularly dangerous because when it comes to infectious diseases like the measles, the overwhelming majority of people have to be vaccinated in order for the vaccination to be effective in society to protect populations like infants or the seriously ill who cannot receive the vaccination for medical reasons.

Read: 4 Easily Preventable Diseases To Eradicate In The New Year

Read: Autistic Brains Are More Symmetrical

Myth: Your blood is blue because it ran out of oxygen

No, our blood is never blue. It is different shades of red depending on how much oxygen it is carrying. Live Science explains that the blood only appears blue in the veins of our arms, for example, because we are seeing it through several layers of tissue — it’s sort of a play on light, as red-colored light does not penetrate the tissue as well as blue-colored light. Blood rich in oxygen is bright red and blood depleted of its oxygen, after delivering it throughout the body, is darker red.