For your consideration...
It is my opinion that changes in my own life style have caused me to be healthier and while some of these ideas are backed by scientific research, the following information was obtained through my personal observations.
Prior to my undergraduate education I was very cautious of "germs". I would habitually wash my hand very thoroughly after touching doors, before eating, and after coming into contact with other people. Most of the time with harsh soaps and very hot water. I would often shower two to three times a day; once before work, once after my work out, and even again before bed. Much of this behavior came from my father who is insistent on hygiene, and for good reason. Hygiene prevents illness, and that is proven. That being said, the only thing that separates a poison from a cure is the dosage (Thanks Paracelsus).
I found myself getting ill very often. I would almost always catch a cold if one was going around. I would also get more intestinal illnesses too such as food poisoning.
My skin was also in bad shape. I would shower often because I was producing a lot of oils in my skin and my hair. I had acne on my scalp and all over my upper back.My hair dresser would comment on my scalp and so would loved ones around me. I did not have acne on my face as a teen, but I did have it in my hair and on my back. After an afternoon nap, my hair would again be greasy and look unprofessional or dirty! I even sought help from a dermatologist and while the proscribed cream worked, the underlying problem was still there.
(Not me)
During my time at University, I spent a great deal of time learning of the bodies innate defenses to diseases and the elements. The outer most layer of skin dies and becomes a barren wasteland for bacteria. This dry dead skin prevents most bacteria from colonizing your skin, and combined with natural oils you produce prevents many infections. I made a connection to why my skin was covered in acne and itching, it was from over showering and scrubbing my outer skin.
My body was losing its outer physical barrier against infection and elemental exposure when I scrubbed all of the protective layer of dead skin off. As a result, my body had to work over time to replace the oils in my skin which caused me to be more oily than usual. The hot soapy water I was using was also most likely killing the healthy and protective layer of bacteria already on my skin. This is the second layer of defense on your skin. With the good bacteria in place, the other microbes have trouble competing for real-estate on your skin.
To combat the excess oil removal I used less harsh soaps with more natural ingredients and less strong surfactants. Hot water also makes the oils in your skin "melt" and become more fluid, much like butter in a frying pan. This combined with the harsh soap was washing away almost all of my natural oils on my skin. I switched to cold water and I will never go back. My skin has cleared up completely and I no longer suffer from acne on my scalp or back!
I also realized that this outer layer of bacteria was on my hands as well. Being completely sterile and touching a surface unknowingly containing pathogenic microbes or viruses is worse than touching it with hand covered in normal human flora. The outer layer of bacteria helps to block the harmful bacteria from getting hold and setting up shop. I now never use hot water or harsh soaps unless I know my hands have been in contact with especially dirty surfaces. Rinsing with cold water will remove dirt and water soluble chemicals without harming your natural layer of bacteria. When I was over washing and scrubbing, I was removing some of my immune system. My dish washer recently stopped working and I was forced to hand wash my dishes. The use of dish soap and scrubbing I believe contributed to a recent cold I contracted. Prior to this period I was illness free for over three years.
Because I am coming into contact and ingesting more microbes I feel that my gut microbiome is also stronger than before. I now rarely contract diarrhea. The microbes I have been consuming as a result of less stringent hygiene as in my opinion bolstered my natural defense against common pathogens. Much like when one takes antibiotics and destroys their normal gut flora they contract intestinal diseases, I did not have a very strong coat of bacteria in my gut or at least a healthy variety and as a result I was getting sick more often.
Mice raised in a sterile environment grow up with hindered immune systems and deficiencies compared to mice raised in normal conditions. https://irp.nih.gov/catalyst/v19i4/germ-free-mice
Of course, this doesn't mean never clean. Keep good cleanly habits but be weary of destroying your bodies immune system in the process. I know for at least me personally, changing my habits improved my way of life considerably. While not contracting diseases may have been luck, although 3 years is a stretch, my skin and the removal of microbes causing acne on my back and scalp were 100% due to over use of shampoo and hot water. I know this because when I trick myself into using the harsh soaps and hot water, at least for me I get sick more often and my skin is in poor shape afterwards.
My opinion is that you should be just as worried about your microbiome's health as you are about your own health, because in fact you and your microbes are one in the same. I think this may be a common problem in today's obsession with cleanliness.