Green’s Dictionary of Slang

(Aus.) acne.

1982		N. Keesing Lily on the Dustbin 176: ‘Zits’ or ‘ackers’ (pimples) may be ‘subterraneous’ or ‘volcanos’ and acne sufferers have faces ‘like a festered pickle bottle’.
1987		D. Oswald Dags 1: Full-scale ack-attack — face like a relief map of Switzerland, you know.
2000		‘Language Talkback’ at www.cltr.uq.edu.au Oct. 🌐 There are many types of diminutives in Australian English [...] acker: acne (=a pimple).