Hygiene is the practice of maintaining health and prevent the spread of disease to others. This is usally done threw multiple ways. Washing your hands, taking a shower, brushing your teeth, etc. Those are what people think when we hear hygiene.
Hygiene can keep us all healthy and pleasent to be around. In addition it helps the health of yourself and others. Practicing good hygiene habits allows a lower spread of harmful bacteria and viruses.
Washing your body - Get all the dirt and grime off your body. Humans are filthy.
Wearing clean clothes - You may be able to get away with it ocasionaly but people may still smell you.
Getting Sleep - This one is less known, this can make you look not dead when you are walking around. In addition sleep is good for your well being.
Cleaning youe nails - So many things get trapped in and under your nails. Clean them so you don't get some form of infection.
WASH YOUR HANDS - I don't think I need to say more. Washing your hands gets all the bacteria from everything you touched for the day.
Many reasons could lead to a person not caring about hygiene. I believe the most common reason is just having to go out of their way to care about themself. Life does have it's hardships. Another could be the person thinking that they could skip a day. This may be true occasinally but not all the time, people will catch on.
The way to practice good hygiene is actually really simple and easy. At least once every couple days take a shower. Brush your teeth in the morning. Wear clean clothes, Wash your hands after using the bathroom, before eating, etc. When washing your hands, be sure to clean under your nails and other little crevasses. Be sure to sleep, if thats at night or day, at least 8 hours of sleep. You don't want to look like a zombie, unless it's for a cosplay.