I wouldn't know either if I didn't study skin physiology. And there is so much to learn. One thing we can rely on is always google.
Credit: nopimplesnomarks.com
Note that some brands don't reveal their full ingredients list to consumers. Some will advertise and claim that they are organic. Yes, they contain organic ingredients that end up right at the end of the INCI list, which probably doesn't have enough amount to do much on the skin.
And yes, whatever ingredient that is ranked at the front of the ingredients list means they have the largest amount percentage.
Credit: The Conscience Fund
Let's take a look at the ingredients in my current cleanser which I have been using for 7 months and not having the slightest thought of changing yet.
Aqua [Water], Glycerin, Caprylic/capric triglyceride, Ethylhexyl palmitate, Cetearyl alcohol, Glyceryl stearate, Argania spinosa kernel oil, Rosmarinus officinalis (Rosemary) leaf extract, Salvia officinalis (Sage) leaf extract, Thymus vulgaris extract, Rosa moschata oil, Sodium lauroyl glutamate, Stearic acid, Decyl glucoside, Xanthan gum, Sodium benzoate, Sodium dehydroacetate, Phenoxyethanol, Parfum [Fragrance], Lactic acid.
Capric/caprylic triglyceride is a common emollient and also a highly popular dispersing agent, and is often used as a vitamin solvent. It is often used for the production of soap, due to its function as a superfatting oil. Some benefits of caprylic/capric triglyceride include the fact that it is not greasy at all, and has a very light texture. It is also rapidly absorbing, and is highly skin-compatible, due to the fact that it will not aggravate sensitive skin types. It also does not leave behind visible oil remnants on the skin.
As you can see, the ingredients in this particular product contains almost all natural ingredients, except for Phenoxyethanol (a form of preservative), which is approved by ICEA. It is used to replace paraben, glycerol or essential oils which some people will develop a reaction to. The percentage present in the product is extremely low; hence it will not impose any negativity on the skin..
The ingredients to avoid:
Parabens
SLES
Silicones
Petroleums
Paraffins
PEG
All the above interferes with the skin barrier's (stratum corneum) natural defense and functions.