不知痛癢

numb / unfeeling / indifferent / inconsequential

no; not so / (bound form) not; un-

not to know / unaware / unknowingly / fig. not to admit (defeat, hardships, tiredness etc)

to know / to be aware

ache / pain / sorrow / deeply / thoroughly

pain and itch / sufferings / importance / consequence

to itch / to tickle