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Skeletal fluorosis is a somewhat more severe adverse health impact, characterized by increased bone mass and bone density (osteosclerosis) that occurs due to a prolonged period of exposure to fluoride at the time of bone modeling and/or remodeling. Fluoride exposure of more than 4 mg/L concentration may lead to skeletal fluorosis; the exposure may be either direct (ingestion) or indirect (inhalation) (Yadav et al. 2019). Skeletal fluorosis occurs in three stages: initial, intermediate, and final:

1 The initial stage – The initial stage shows various mild symptoms like joint pain, stiffness of bones and joints, muscle weakness, periodic pain, and chronic fatigue.

2 The intermediate stage – The intermediate stage is characterized by calcification of bone followed by hardening and stiffening of joints as well as calcification of ligaments in the body. Patients may develop a “Poker back” situation in severe cases of skeletal fluorosis.Poker back‐ a condition in which the whole spine becomes a fixed column due to increasing bone stiffness.

3 The final stage (crippling skeletal fluorosis) – In this stage, joint movements become very limited and skeletal bone deformities, acute calcification of ligaments, muscle wasting, and neurological defects can be seen in patients (Itai et al. 2010).

According to some literature, it has been revealed that maximum ingestion fluoride ions can cause other health effects such as headache, deformities in red blood cells, rash over skin, gastrointestinal problems, depression, low haemoglobin levels, nausea, pain in abdomen, fingers and toes with tingling sensations, and reduced immunity, as well as neurological manifestations which are quite similar to pathological changes occurring in patients with Alzheimer’s. These effects of fluoride have received less attention in comparison to the dental and skeletal fluorosis typical of high fluoride‐contaminated areas (Thole 2013).