Sodium lactate doesn't break down into lactic acid. It's kinda the other way around.
Lactic acid + NaOH --> Sodium lactate.
Sodium lactate + water --> sodium ions + lactate ions.
Same thing with calcium lactate, only it releases calcium ions in water, not sodium.
I would not add calcium lactate to soap. Calcium ions bind with soap to form sticky insoluble soap scum. This reduces the cleaning ability of soap and leaves a sticky film on the skin. You don't have to deliberately add calcium lactate to soap to learn what calcium does -- just bathe with soap and hard water.
If you feel the need to experiment, adding calcium lactate to soap won't cause harm in the sense of being toxic or causing an explosion or things like that. This is a quality issue, not a safety hazard.
Hi Sonny, Good logical question. 1) Yes Calcium lactate is definitely soluble in water, at the rate of 4.8g/100ml (10c), 5.8/100/ml (20c), 6.7/100ml (25c), 8.7g/100ml @(30c), and 7.9g/100ml @30c. 2) While the Na salts (soaps) of fatty acids are highly soluble, the Ca, and Mg salts (soaps) are typically described as insoluble. But, to be scientifically accurate, they do have a VERY slight, barely measurable degree of solubility. Solubility depends primarily on the length of the fatty acid, and the number of double bonds. The solubility of highly saturated magnesium stearate (12:0) is only 0.004g/100ml @25, while the mono-unsaturated oleic acid, 18:1 (18 carbons:1 double bond), is slightly more soluble. Remember, also, while Na soaps contain only ONE fatty acid, Ca soaps contain TWO fatty acids.
And, as DeeAnna pointed out, if you have "hard" water, the insolubility of Ca & Mg soaps is clearly apparent, every time you try to clean your bathtub, or shower.