There are various forms of toxicity caused by exposure to woods through dusts or by direct contact. You can develop allergies following contact by touch or through the inhalation of dust. In other words, both large and small particles can sensitize you to the allergen. The reaction can be a skin or lung reaction.
Skin reactions are generally itchy rashes.
Lung reactions are generally chronic coughs or wheezing. Other types of problems come from chronic exposure to dusts that are small enough to reach the small airways and alveoli. Dusts larger than 10 microns settle out in the upper airways. Less than 0.1 micron particles are so small that they don't settle anywhere very much. They go in and out.