1660s, "black mark, stain," from verb smutten "debase, defile" (late 14c.), later "stain or mark with soot, etc." (1580s), cognate with Middle High German smotzen "make dirty," from West Germanic *smutt- (source also of Middle High German smuz "grease, dirt;" German Schmutz "dirt," schmutzen "to make dirty"). The meaning "indecent or obscene language" is first attested 1660s.
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy).
<a href="https://www.etymonline.com/word/smutty">Etymology of smutty by etymonline</a>
Harper, D. (n.d.). Etymology of smutty. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/smutty