Updated, and I will be adding to this post.
The ideal of using the most natural hair care products is a very appealing one from a number of perspectives. The reality can be quite different. With any cosmetic product it comes down to formulation, ingredient choices and proper, safe manufacturing practices regarding results. Even all natural soaps need to be carefully made to avoid caustic free alkali causing problems in the end product.
Sulfate-free shampoos are marketed to be preferable for hair care because the cleansers are more mild and less irritating than sulfates. Are they really though? I have read many reviews of sulfate-free shampoos and there are multiple reports of very dry hair and irritated scalps. It is about the sulfate-free cleansers used and their combination with other ingredients that determines the outcome of product use. That applies to sulfate shampoos too.
Sulfate shampoos have been used for many years without problems and continue to be available today through many companies that offer sulfate-free options. Sulfate-free, paraben-free products are big business right now.
However, sulfate-free can be tricky to define at times. C14-16 olefin sulfonate is used in a number of "all natural" shampoos and it can be a harsh cleanser that is not what I would call natural. In fact, shampoo cleansers while derived from natural sources in many cases, including the mild sulfate, sodium laureth sulfate are created in laboratories, with processes that vary in artificial additives.
A less publicly known problem with the most popular sulfate-free cleansers, alkyl glucosides is that they can be potent allergens, causing allergic contact dermatitis. Botanicals used in conjunction with these cleansers, plus fragrance and other additives, individually and in concert can cause one to react to a shampoo and not have a clue as to what exactly may have caused their reaction. Allergy tests can be done. Showing the ingredient list to a dermatologist can be a good idea too, as he or she may spot other known allergens to test first, saving time.
Parabens and sulfates came under a lot of controversy because of certain research studies, and concerns regarding cosmetic ingredient contamination. Specific parabens have recently been reaffirmed for safety as used in cosmetics in Europe, two with a recommendation that they be used at less concentrations than previously allowed and restricted in use, while others have been banned until further assessment has been made. See updated References below.
The contamination issue, regarding 1,4 dioxane, a by-product of the manufacture of a number of cosmetic ingredients has been and continues to be monitored by governments regulating cosmetics. Government regulation stringentness of cosmetics varies in some countries. However, the safety of cosmetic ingredients makes the news and is online too from reputable sources, as well as from scare tactic marketing hype sources, that want nothing more than to sell you their products.
Preservatives are a necessary part of cosmetic formulations to prevent the growth of bacteria and yeasts that can cause problems for the user if not present. I for one am not fond of of a shampoo or other cosmetic product going off and I toss the product if that occurs.
Other preservatives have come under scrutiny for safety, like phenoxyethanol for example, widely used in cosmetics, including those that claim to be all natural. The point is that cosmetics ingredients are monitored, scientifically studied and regulated, and consumers are not victims. Are there improperly formulated cosmetic products on the market? Yes. Some "fly under the regulations radar" and are homemade but sold online and locally. Some are smuggled into countries from countries with few cosmetic regulations on safe cosmetic manufacturing. These are exceptions and many of the latter can be found on government Advisories and Recall lists in the United States, Canada, and other countries.
References
"Antiperspirants and Breast Cancer Risk", 2014, bolding added by me
http://www.cancer.org/cancer/cancercauses/othercarcinogens/athome/antiperspirants-and-breast-cancer-risk#.VfbzFej2pdQ.twitter
"so far, studies have not shown any direct link between parabens and any health problems, including breast cancer."
"Parabens", 2015
http://www.rsc.org/chemistryworld/2015/06/parabens-podcast#.VfbG1IHjE6A.twitter
"European Commission - PRESS RELEASES - Press release - Consumers: Commission improves safety of cosmetics", 2014
http://europa.eu/!hU34kN
"Propylparaben and Butylparaben, other parabens ... Methylparaben and Ethylparaben, are safe ... Commission limits the maximum concentration of ... Propylparaben and Butylparaben, from currently allowed limit of 0.4% when used individually and 0.8% when mixed with other esters, to 0.14% ... used individually or together. They are being banned from leave-on products designed for ... nappy area of young children below ... age of three since existing skin irritation and occlusion may allow increased penetration than intact skin ... new rules ... apply for products ... on shelves after 16 April 2015 ... Commission banned ... five other parabens in cosmetic products - Isopropylparaben, Isobutylparaben, Phenylparaben, Benzylparaben and Pentylparaben ... due to ... lack of data necessary for reassessment."
http://www.rsc.org/chemistryworld/2015/06/parabens-podcast#.VfbG1IHjE6A.twitter
"European Commission - PRESS RELEASES - Press release - Consumers: Commission improves safety of cosmetics", 2014
http://europa.eu/!hU34kN
"Propylparaben and Butylparaben, other parabens ... Methylparaben and Ethylparaben, are safe ... Commission limits the maximum concentration of ... Propylparaben and Butylparaben, from currently allowed limit of 0.4% when used individually and 0.8% when mixed with other esters, to 0.14% ... used individually or together. They are being banned from leave-on products designed for ... nappy area of young children below ... age of three since existing skin irritation and occlusion may allow increased penetration than intact skin ... new rules ... apply for products ... on shelves after 16 April 2015 ... Commission banned ... five other parabens in cosmetic products - Isopropylparaben, Isobutylparaben, Phenylparaben, Benzylparaben and Pentylparaben ... due to ... lack of data necessary for reassessment."