What is the chemical structure of the cocoate ion vs. the olivate ion? I am wondering how the cocoate ion (in natural soaps, in the form of sodium or potassium cocoate and from the saponification of coconut oil) differs structurally from the olivate ion (from the saponification of olive oil)?

My family is attempting to implement the methods in solveeczema.org and believe that our children have detergent-reactive eczema and our baby is most sensitive.  In moving away from detergents and to natural soaps, we have started using soaps that result from the saponification of vegetable oils - mostly coconut oil, palm kernel oil, and olive oil.  We discovered that our other child (a toddler) seems to react to these soaps in a similar way that he would react to a cleaner containing much stronger/harsher surfactants (such as sodium lauryl sulfate).

Our toddler seems to get bad eczema flares using soaps that contain cocoate, but he has no reaction to soaps that contain 100% olivate.  I have no idea why this would be, since I would assume that both cocoate and olivate have the R-COO- structure.  Is cocoate much more hydrophilic than olivate?  Is the functional group different?  Is the cocoate ion a longer molecule that looks much more like a harsh detergent than a salt resulting from saponification of olive oil or tallow?

Please note that this question is related to two questions already asked:

1)  Is soap the natural form of Sodium Lauryl Sulfate?

2)  https://parenting.stackexchange.com/questions/5047/how-to-test-whether-my-toddler-is-allergic-to-detergent/5049#comment7644_5049
Note 1. Both coconut oil and olive oil are natural oils. The soap, produced from them, is mixture of several compounds.

The difference of olive and coconut oil may be easily found in wikipedia: http://en.wikipedia.org/wiki/Coconut_oil#Composition_and_comparison 

In short, coconut oil contains mostly saturated acids esters, while olive contains mostly unsaturated ones. The unsaturated acid esters are responsible for olive oil ability to solidify on air. But here is 

Note 2: In my knowledge, allergy is usually caused by carbohydrates or proteins. Fatty acids and their ions have too few binding sites to be recognized by immune system as something distinct from our own. The real source of reaction may be 


Minor components of initial oil. There are quite many of them and removing them completely is not easy. 
Other components of soap, such as perfume or pigment.
Soap solution pH, that may differs from soap kind to kind, but this is unlikely.