40d:Cave adaptation

Cave adaptation is a condition that happens to your dwarves after spending too much time underground. It is unclear as to how much time underground causes cave adaptation, and there is no way to tell if a dwarf has cave adaptation simply by looking at their various stats.

When a dwarf with cave adaptation goes outside, the dwarf will gain one of two negative thoughts. If the dwarf has mild cave adaptation, he will gain the thought 'irritated by the sun recently', and suffer no other effects. A dwarf with serious cave adaptation will gain the thought, 'nauseated by the sun recently' and will vomit all over the ground. While vomiting a dwarf is unable to defend himself, which can be a problem during combat.

A dwarf with the description, 'likes working outdoors and only grumbles mildly at inclement weather' is no more resistant to cave adaptation than a regular dwarf is. Likewise, dwarves that like working outdoors may even have cave adaptation.

Fortunately, cave adaptation is not a serious issue. The unhappy thought from even serious cave adaptation is not particularly strong, although you may want to keep very unhappy dwarves inside so the thought doesn't push them over the edge. Dwarves who vomit all the time don't seem to get hungry any faster.

If your trade depot is outside, cave adaptation can create the amusing scene of thirty dwarves carrying goods to the depot all emerging and throwing up at once. Fortunately, the merchants seem to take this in stride, and don't allow it to negatively affect negotiations.