An additional difficulty is that trees vary within a species. One specimen may contain low levels of its toxic agent and the next contain much higher levels. So experience may not be a reliable guide. The main effect is irritation . This can be caused by skin contact with the wood, its dust, its bark, its sap, or even lichens growing on the bark.
Irritation can, in some species of wood, lead to nettle rashes or irritant dermatitis.
On average, they take 15 days to develop. Symptoms usually only persist as long as the affected skin site remains in contact with the source of irritation, eg wood-dust. Symptoms subside when contact with the irritant is removed. Sensitisation dermatitis is more problematic and is usually caused by skin exposure to fine wood dust of certain species. This is also referred to as allergic contact dermatitis and results in similar skin effects to those produced by skin irritants.