The measurement and control of humidity is imperative for environments including medical (e.g. diagnostic tools, operating theatres, rehabilitation wards), manufacturing (e.g. glasses, coatings, optical fibers), agricultural (e.g. greenhouses, crop fields), food (e.g. baking, drying, storage) and buildings (e.g. museums, heritage buildings).  Recent advances in humidity sensors that are both fast and sensitive are discussed. Optical sensors are inherently immune to electromagnetic interference. In-house fabricated planar optical sensor heads can reach a sensitivity of 310 nm/100%RH (e.g. 6×10^-3%RH detection limit). In-house developed fiber-optic sensor heads can achieve a response time of 3 ms, which is the fastest ever reported. A new type of touchless control based on humidity signals is also presented, which can compete against sound- and gesture-based technologies, with unique applications.