Differences between ひ弱い and か弱い

Question

How did the prefixes ひ and か come about and what are the differences in meaning between ひ弱い and か弱い?

Are either of the prefixes pejorative like how ド is in the examples in dainichi's answer to 'Where does the ド in ド素人 come from?' ?

They both seem to emphasise or strengthen the meaning of 弱い but how are they different in extent or nuance? What are the situations where you would use one but not the other?

(On the grammatical side of things, I noticed ひ弱い, ひ弱な, か弱い but not か弱な. But I'm not sure if か弱な appearing to be forbidden has any significance.)

Also, I came across a か細い. Are the prefixes productive? (Can I also form a ひ細い? Or prefix か or ひ to other adjectives? It would appear not since ひ細い doesn't have a dictionary entry )

Answer 1

ひ弱 is usually straightforwardly negative and derogatory. The word sometimes has the implication of "sickly".

か弱い often refers to a type of weakness that stirs someone's sympathetic feeling or protective instinct. か弱い is not necessarily negative, and you can even find articles that says か弱い女性はモテる, in which case the nuance is more or less close to that of 小動物系 or はかない系 (please use google image search). Other か弱い beings might include an infant, a Chihuahua, the little match girl, Cinderella, etc.

Grammatically, ひ弱 is normally used as a na-adjective, and か弱い is always used as an i-adjective. ひ弱い腕 may not be wrong, but ひ弱な腕 is much more natural and common. か弱な腕 is plain wrong.

Dictionaries say ひ and か are indeed prefixes, but these are fairly rare and it's impossible for me to generalize their usage. They are not productive, and I cannot think of other adjectives that contain the same prefixes.