swelling of the lymph glands
痤 centers on a specific medical condition: swelling of the lymph glands. It is a narrow, technical term without broader abstract extensions.
痤 combines the sickness radical 疒 with 坐, which likely contributes the sound. The exact historical development is uncertain.
The sickness enclosure 疒 wraps around 坐 (sit). Picture a person sitting uncomfortably because of swollen lymph glands.
For サ, imagine a swollen gland that looks like a small sack: sack -> サ, and the sickness enclosure holds the swelling.