While real leather seems to be a natural product that shouldn't emit many odors other than its original scent, the fact is that many chemicals are used to process leather, and many of these emit odors. The rest of that leather sofa has plenty of other chemicals in it, and their odors linger long after the manufacturing process and often even after you bring the furniture home. There's no instant way to get rid of these funky smells, but time always helps. The best way to get rid of the odor is to air out the sofa in a room on its own with windows open and fans operating as the weather permits.
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A Soup of Leather-Tanning Chemicals
Unless you buy naturally tanned leather, it requires a slew of chemicals to tan leather to get it to the stage where it's ready to become upholstery. Even the highest-quality leather goes through intensive chemical processing to get it to its final finished stages. Up to 48 chemicals are used to tan leather, including formaldehyde. Many of the chemicals off-gas or emit fumes for quite a while, and some of these chemicals are somewhat toxic. Part of that "leather smell" is actually the chemicals used to tan the leather, so it's best to let your leather sofa air out for as long as possible before using it.
Faux leather, blended leather, and other types of leather also contain all sorts of chemicals that could emit odors. The dye used to color leather or any faux leather is another source of chemical odor. Any treatments used to protect the upholstery also emit odors, so there's quite a list of chemicals that could cause foul smells in just the upholstery alone.
More Chemicals From Manufacturing
Furniture manufacturers use all sorts of materials to make a leather sofa besides the actual upholstery. The frame inside, the adhesives used to hold various materials together, and the batting and cushion beneath the leather are all potential sources of noxious odors emanating from your new sofa. Since there's no real way to deodorize something you can't access within the sofa, these items may emit slight odors for quite some time.
The best thing you can do when the sofa is brand new is to remove any plastic or nonbreathable wrapping materials used to keep the sofa and its cushions clean. Plastics simply hold in the odors. Once the plastic is off, the odors have a chance to dissipate.
Removing the Chemical Smell
Once your new sofa arrives at your house, you may be tempted to set it up in its ideal location. If you really want to remove as much stink as possible without smelling the stench in other areas of the room, set the sofa in another protected area, such as a clean garage, for a few days with the garage door open while you're home and during daylight hours. A screened-in porch is another option. Such locations allow ample airflow to circulate around the sofa, which helps the odors trapped within it to escape. If the cushions come off, remove them, and if they unzip, open them and let them air out. Even remove the inner cushion if it looks like you can take it out in one solid piece.
If you can't set the sofa in a garage or on a patio, a spare room is another good choice since you can open the windows and close the door. When there's no choice but to leave the sofa where it belongs, you can still open windows, remove cushions, and turn on fans for better air circulation. Sprinkle baking soda liberally over the sofa, the cushions, and the base beneath the cushions if possible. After 24 hours, vacuum up the powder. The baking soda absorbs odors, so the sofa should smell somewhat better. If necessary, sprinkle more baking soda on the sofa and leave it for a couple of days before vacuuming.