"Epigenetics changes" or "modifications" cause different kind of changes that affect how a person's genes work or 'express themselves' in three different ways (called "epigenetic mechanisms"), but do not change the gene in the DNA. These epigenetic changes may be inherited, or they may happen "in utero" which is when a baby is still inside its mother. They may also happen in childhood, because of different reasons, like a respiratory infection, being exposed to chemicals or drugs, diet etc. These changes can be passed from one generation to the next but are not permanent and might only be passed down one or two generations. Even though epigenetic changes affect how a person's genes work they do not permanently change a person's genes. It is believed epigenetic changes may also make a person more likely to get certain diseases like asthma.