If two effects are correlated, then three possible causal relationships are possible.

A first effect may cause the second, or the second may cause the first, or a so-called third variable may cause both.

It is possible that an individual who has been afflicted by certain difficulties is more likely to participate in sex work.

It is also possible that individuals from certain populations are more likely to participate in sex work, and also, due to being associated with the population, are also more likely to be afflicted by certain difficulties.

Both possibilities must be considered as alternative to sex work causing such difficulties, to explain the correlation.