The definition of detoxification is removing potentially harmful toxins from the body. We are all affected by things that we daily come into contact with that contain toxic particles.
Here are some examples:

Pollution - in the air and water
Non-stick chemicals - non-stick cookware, stain resistant fabrics
Xenoestrogens - insecticides, lubricants, adhesives, paints, personal care products (red dye no. 3), weed killer, sunscreen lotion
Human growth hormones fed to cows to increase milk production
Plastics - containers, water bottles, baggies
Food - pesticides on fruit and vegetables, processed foods, refined oils
Faucet water - chlorine, heavy _meta_ls, chloroform, etc.
Personal care products - anti-bacterial soap, perfumes, creams, shampoos, lotions and other similar products have a range of toxins like artificial fragrance, Benzaldehyde, benzalkonium chloride and sodium laureth sulfate
Amalgam dental fillings (source of mercury) and dental sealants
Household cleansers
Pre_script_ion, recreational and over-the-counter drugs
Dry cleaned clothing allergens, and antibiotics.

Regular exposure to these things can prevent your body from functioning in its full potential, and potentially cause disease. If you are experiencing any of the following symptoms, it is possible your body would benefit from a detox:

Acne, Frequent, unexplained headaches or back or joint pain, or arthritis, chronic respiratory problems, sinus problems or asthma abnormal body odor, bad breath or coated tongue, food allergies, poor digestion or chronic constipation with intestinal bloating or gas, brittle nails and hair, psoriasis, unexplained weight gain over 10 pounds, unusually poor memory, chronic insomnia, depression, irritability, chronic fatigue, environmental sensitivities especially to odors, or an inability to conceive or carry a baby to full term.