There is no official medical advice on this matter, taking regular showers doesn't yield any known health benefits. Except for certain specialized professions e.g. in the medical field where you need to be sterile, you don't need to take showers except possibly for social reasons. Not taking showers, however, may yield health benefits. While not proven, there are biologically plausible arguments in favor of not taking showers.
Let's start with the reason why most of us take showers. This is not because we're following medical guidelines to prevent certain illnesses, it's simply a matter of us not wanting other people to smell us from a large distance. This smell is caused by bacteria that grow in our sweat, they produce chemical compounds like butyric acid that have a strong smell. As explained here these smells have a biological function in animals.
In our modern lifestyle, we have eliminated this flora on our skin and we're also less exposed to bacteria in our environment. This has been linked to the increased frequency of allergies that we suffer from. As pointed out here:
The results were incredible. Like most of us in the Western world, the families had far fewer types of bacteria living in and on them when compared with people in traditional tribes in parts of the developing world. One hunter-gatherer community was found to not only have a higher diversity of bacteria, but only one in 1,500 suffered from an allergy - compared with one in three in the UK.
Now, taking regular showers combined with and the general approach to hygiene in the Western world may be implicated in many other health problems. E.g., recently Parkinson's disease has been linked to changes in the gut flora. Now, this does not mean that taking regular showers will lead to some illness, but it's also not easy to rule this out. Someone who is healthy who gets some stomach bug for which antibiotics are prescribed may lose a lot of his intestinal microbes; the fact that he like almost everyone else takes regular showers and lives in a very clean environment may then predispose him to his gut flora to get populated by the wrong type of microbes which may cause problems down the line.
So, while we can't say that taking regular showers has been proven to be harmful., the opposite that it's healthy can't be proven either, and from a broader perspective there are far more reasonable, plausible arguments to suggest that you should not bet on it being good for you.
The real question that should be addressed is how we can stop taking regular showers in a socially acceptable way, because the only reason why we take showers is for social reasons, not for health reasons. Now Dave Whitlock has done an experiment, demonstrating that it's perfectly possible to not take any showers at all:
Showering, for many of us, is an important part of our daily routine. Personal hygeine is a good thing to maintain if you want friends or a job.
However, Dave Whitlock, a chemical engineer, has decided to eschew bathing for 12 years in favour of dousing himself with a live bacteria spray, invented by a company he co-founded.