Outdoor footwear will last longer - and smell better - if treated with proper care. Some types of footwear (sandals) just need to be kept clean, but others (hiking boots) may need additional conditioning or waterproofing treatments.
Sandals, especially those with polyurethane footbeds, are notorious for acquiring an unpleasant odour after a bit of use. Make sure to clean them early and often to prevent odours from taking hold. Soak the sandals for several minutes, and then scrub away the grunge that gets embedded in the footbeds with a little detergent in warm water. (An old toothbrush makes a good scrubber.) Suede footbeds should not be scrubbed too aggressively.
If the odour persists, try scrubbing with baking soda and salt water, followed by a fresh water rinse. There are also products like Sandal Suds designed to clean synthetic sandals and eliminate odours.
Boots can get pretty dirty. To clean them, remove the laces, scrape off caked-on mud, and brush off superficial dirt with cool water and a cloth. Then scrub with a soft brush to remove ground-in dirt and rinse well with cold water. Air-dry wet boots at a moderate temperature. Do not dry them close to a heat source, such as a campfire or wood stove.
Wash boot linings with gentle soap, to rinse away accumulated salts, then allow them to dry. Leather linings can be treated with conditioner to enhance breathability.
Leather uppers are just like skin, if they're not conditioned, they dry out, stiffen, and crack. Conditioners restore lubricants to leather and keep it supple and, depending upon the conditioner, waterproof.
Wear new, untreated boots a few times to remove the factory-applied buffing wax. Before applying a conditioner, ensure your boots are dry. While conditioning, pay special attention to the crease in the upper where your toes cause the sole to flex. This crease can crack if left untreated.
Both silicon and wax treatments can be water-based. This means they work best when applied to damp boots. The water in the pores of the leather acts as a conduit for waterproofing agents that absorb into the leather as the boots dry. Water-based treatments are popular for full-grain (rough-out) leather, nubuck, and suede leathers, as well as fabric and boots with Gore-Tex® lining.
Waxes are the most frequently used treatments, although they can darken leather, especially rough-out hides. This may detract from the appearance of the boot. Waxes work best when applied thinly and evenly with your fingers. Some treatments can seal leather so effectively that it compromises breathability. If you're hiking in really soggy conditions, this might be a satisfactory trade-off.
Best applied when your boots are new and unworn. Silicon will not darken or discolour leather or fabric. It allows better breathability for leather footwear than wax treatments, but may not condition as effectively. Wax-based treatments that contain silicon offer excellent water repellency and durability, but will discolour rough-out, suede-style, and synthetic fabrics.
Fluorochemical treatments are non-aerosol pump sprays designed to work on all types of footwear, especially those made of suede or synthetic fabric. Fluorochemicals added to silicon treatments offer excellent durability and will not discolour the boot material. These are not the same as volatile, ozone-depleting CFCs (chlorofluorocarbon).
Some oil-based treatments (Neatsfoot oil, saddle soap, dubbin) stretch leather, which compromises the stiffness and support of a boot. Leave these kinds of treatments for breaking in your baseball glove.