It depends on how much and what sort of activity you do, how clean your environment is as well as what kind of climate you live in.
From a strictly health point of view you could shower only once a week or even once every 2 weeks without any obvious health problems. Although you would be very smelly and dirty.
The more activities you do and the hotter and dirtier your environment is, then the more frequently you need to shower.
skip a day shower skip a day shower...
At least once daily thoroughly, face twice, and hands several times daily.
A better more, healthy way is to shower daily and wash your hands before you touch your face or any food. You should ALWAYS shower with warm water, soap, and wash your hair with Shampoo and Conditioner. Use dandruff controllable shampoos if you have dandruff on your head. If you have poor hygiene Then shower often and remember to wash your hair, use soap and warm water. The main things you need to do for your hygiene is to brush your teeth at least twice daily, wash your hands before you eat or touch food (or your face), wash your face too, and shower often. Use combs and brushes to get knots and tangles out of your hair but conditioner can help you do that. If you have straight hair then you can towel dry but if you have a perm, blow-dry. You can find cheap blow-dryers if you don't have one. The best place to buy them is at Wal-Mart.
Answer
It really depends on your body. I have a child with eczema and she can only shower 2x a week. The more you shower and the type of soap you use also can dry your skin out. For over weight people they should shower more making sure they pay attention to folds of skin, bacteria and yeast like to get trapped there. Personally I think you should shower every other day at least unless it is hot and you have been sweaty then shower definitely.
If you use products like gels or hair spray in your hair you need to wash your hair everyday. However if you have dandruff then you should not be using these products and should wash your hair once or twice a week. Dandruff is usually caused due to dry scalp or not rinsing your hair well. I do not use conditioner due to the fact I do not style my hair on a daily basis and so I am not stripping it of it's natural oils. I also do not have dry scalp. Therefore to put conditioner in my hair is to make it oily. If you have dry scalp or brittle, dry hair Yes you need conditioner. Apply it in the shower after you have washed and rinsed your hair, then with conditioner in your hair COMB your hair. This removes the hard tangles and insures the conditioner is all the way through
your hair and on your scalp. Then wash your body and let it sit in your hair to give it time to work. Rinse your hair last and then get out and dry off.
Hope this helps anyone who may need it.