Resin is toxic. Fumes are very harmful, very irritant and you need to use proper protection. Goggles, mask, filter and gloves (non-latex, as latex will burn)
Polyurethanes like Polyesters present their own hazards and you should familiarise yourself with them before use. Approved respirators, gloves and good ventilation should be observed at all times.
It is harmful to the enviroment, toxic, irritant and corrosive (means will burn through some surfaces, including your hand!)