Does poor hygiene cause acne?

Usually not a cause: Acne occurs when skin glands produce more oil, but the openings of the glands are blocked by little plugs of dead skin cells (comedones). Skin oils leak sideways into the skin, causing inflammation that brings in lots of white blood cells, forming a pustule. Not washing enough usually doesn't cause acne. Causes include hormonal changes, emotional stress, certain medicines, skin rubbing, etc...

It may make worse : Poor hygiene may lead to increased pore obstruction and bacterial growth which can exacerbate acne although it may not necessarily cause it.