This isn't a direct response to your question, which is whether no-poo/no-soap is physically healthier. This response is intended to point out that it may be socially damaging: keep in mind that some people may believe they don't smell when they don't use soap because they can't perceive androstenone.

Reportage in the popular press in 2007, referring to studies: http://www.sciencedaily.com/releases/2007/09/070916143523.htm and here: http://www.sciencedaily.com/releases/2007/10/071030080645.htm

I haven't been able to find anything relevant yet about improving skin health by abandoning soap.

EDIT: This article kind of hints that soap might not be a miracle cure: "Current data contradict some historical classifications of cutaneous microbiota and suggest that these organisms may protect the host, defining them not as simple symbiotic microbes but rather as mutualistic." http://www.ncbi.nlm.nih.gov/pubmed/18275522

FURTHER EDIT: The buzz phrase is "skin microbiota." See this article here: http://genome.cshlp.org/content/early/2008/05/23/gr.075549.107.full.pdf It looks like work is just getting started. Apparently there is lower diversity in skin microbiota between people than there is in gut microbiota. I would caution against overanalogizing.

STILL FURTHER EDIT: People with more diverse skin microbiota may, repeat, may be less appealing to malaria-carrying mosquitoes. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028991

I don't know if there's a scientific basis, but anecdotally -- I stopped washing my hair with anything but water about two months ago, and I have definitely noticed that it doesn't get oily any more. I never had super-oily hair to begin with, but it's long and thick, and I used to notice things getting a bit greasy after 1 to 2 days without shampooing it. Now I only rinse it with warm water about 2 times a week, being careful to massage the scalp and brush it out afterwards, and I have found that I can go as many as 5 days before it starts to look even slightly oily.

Not Scientific:

No Shampoo for me. Baby fine oily hair to start with. It's working out well so far. I use soap on pits, tits, bit's, and feet only unless I'm actually dirty. I exfoliate my face with sugar and honey twice a day and follow up with an aloe based moisturizer. When I've had experimental breakouts with dairy, they heal up super quickly now. If my skin gets scratched...it heals much quicker. I also don't get razor burn now from shaving. I just use water to shave. I'm sure there are lots of variables, but all of my skin feels healthier now. And my hair is getting much better too.

I am one of the Great Unwashed!

A few years ago, about a year after I fell into ancestral eating, I was thinking about animals in the wild. They all wear sleek, sumptuous furry coats, coats that never carry a coat of grease or need a swipe of deodorant. Animals in nature know how to clean themselves by preening, by dips in fresh water. Why should I be different?

I chucked the soaps and cosmetics and decided to go thirty days without, just for laughs. I can experiment in these ways perhaps easier than most as I am a poet and people expect me to be gross and smelly.

The transition took several months, to be honest. My hair, which extends to my tailbone and is thus considered Damn Long, morphed from Breck Gal with bouncy waves and silicon-enhanced shine to Get-Outta-Town Gal with clumps of sebum-crusted tresses. Not my finest moment, y'all.

I did a procedure called "preening," where I moved my natural oils down the length of my hair using my fingers. I was as careful as a resting cat, as my companion parrot. One small sector of hair at a time. Weeks passed and my hair started looking soft, shiny, full of body, wonderfully REAL. It didn't have the shimmer and bounce of my Breck (and Aveda, let's be honest, I am a Hair 'Ho) days, but it had an integrity.

The rest of my body followed suit. I moved from a perfumed and pampered middle-aged mom to a wild and self-scented Amazon, with long, wild hair, and a Paleo curvy body to match.

Watch out world!

(Yea, this was scientific as shit. I know, I know. But I think you should TRY it. What's the worst thing that will happen? People will just call you a poet.)

I use only shampoo, soaps and moisturizers that I can safely ingest-- I use Dr Bronner's Castille Soap-- and I use it to clean my hair and body (it can also be used as toothpaste and 30 so odd other uses-- it's organic and fair trade, too) For conditioner, I use shea butter or coconut oil. For moisturizers, I use food grade, organic oils--- mainly apricot and coconut oil. My hair and skin are happier than they were previously when I 'pampered' them with expensive (and dangerous!) lotions and potions-- and it's also greatly simplified my beauty routine.

I have very oily dark hair, so when it gets oily it looks like it's wet and it feels waxy and sticky. I have been doing the No Poo since january 2012. I would use a baking soda/water mix as a shampoo every time it got oily and now I am down to using it once or twice a week. I also used a 50% apple cider vinegar mix as a conditioner and it works great. not sure if the health benefits are 100% true but I do know that my hair gets less oily and baking soda is far cheaper than shampoo

I have never heard of any studies. I have found the decrease in oil production happened for me, but it is n=1.

I use a homemade shampoo, which leaves my hair a little more oily, naturally, but nothing unmanageable. I don't know about the science behind it, either, but I'm an oily person and have found that excessive washing leads to even more washing. I've also stopped washing my face, except when I take my evening bath. I've noticed a general decrease in oil on my skin. But I do put coconut oil on it most afternoons as a moisturizer. Is it connected? Maybe. This is my experience, and by no means scientific...

Whether or not it is biologically benificial (which I like to think it is) It has a lot of lifestyle benefits if you like simplicity, as well as economic benefits. My n=1 is that I have super sensitive dry allergenic skin that is happy if I simply don't touch it. That being said I have not been able to give up regular soap on my body, but poo', facewash etc yes.

I use a homemade facial scrub from extra virgin olive oil and castor oil. Here's a website that I really like that gives info about the recipe and how to adjust it for your skin type:

http://www.simpleorganizedliving.com/2011/02/23/homemade-facewash/

It took me a few tries to find the formula that works best for me, but now I love it.

nobody is going to study something that doesn't benefit an industry. the soap and body care industry is ridiculous, and extremely damaging to our bodies, our environment and our psychology. I don't use soap i just skin brush, which is amazing for your skins circulation as well as exfoliates, although anymore i just have smooth soft skin, even after a week of no brushing. I use a maximum of dr. bronners + apple cider vinegar rinse for my hair (its long, I farm, grease+dirt=needs to be washed for real sometimes) I eat a diet high in animals fats, minerals, water and low in carbs, my skin is resilient and does not need moisturizer. it took about 5 years to get to this point and probably would take less for someone with a less compromised system, its well worth it.