tremuloides) sumac (Rhus glabra), spruce (Picea spp.), various pines (e.g., Pinus echinata, Pinus ponderosa), Douglas fir (Pseudotsuga menziesii), larches (Larix spp.), true firs (Abies spp.), hemlocks (Tsuga spp.), cannabis (Cannabis sativa spp.), cedars (Cedrus spp.), various Cupressaceae, and juniper bush (Juniperus spp.). It contributes to the characteristic odor of orange peel, orange juice and other citrus fruits. To optimize recovery of valued components from citrus peel waste, d-limonene is typically removed. Safety and research -Limonene applied to skin may cause irritation from contact dermatitis, but otherwise appears to be safe for human uses. Limonene is flammable as a liquid or vapor and it is toxic to aquatic life. Uses Limonene is common as a dietary supplement and as a fragrance ingredient for cosmetics products. As the main fragrance of citrus peels, -limonene is used in food manufacturing and some medicines, such as a flavoring to mask the bitter taste of alkaloids, and as a fragrance in perfumery, aftershave lotions, bath products, and other personal care products. -Limonene is also used as a botanical insecticide. -Limonene is used in the organic herbicides. It is added to cleaning products, such as hand cleansers to give a lemon or orange fragrance (see orange oil) and for its ability to dissolve oils. In contrast, -limonene has a piny, turpentine-like odor. Limonene is used as a solvent for cleaning purposes, such as adhesive remover, or the removal of oil from machine parts, as it is produced from a renewable source (citrus essential oil, as a byproduct of orange juice manufacture). It is used as a paint stripper and is also useful as a fragrant alternative to turpentine. Limonene is also used as a solvent in some model airplane glues and as a constituent in some paints. Commercial air fresheners, with air propellants, containing limonene are used by stamp collectors to remove self-adhesive postage stamps from envelope paper. Limonene is also used as a solvent for fused filament fabrication based 3D printing. Printers can print the plastic of choice for the model, but erect supports and binders from High Impact Polystyrene (HIPS), a polystyrene plastic that is easily soluble in limonene. In preparing tissues for histology or histopathology, -limonene is often used as a less toxic substitute for xylene when clearing dehydrated specimens. Clearing agents are liquids miscible with alcohols (such as ethanol or isopropanol) and with melted paraffin wax, in which specimens are embedded to