Cell Thumb Replaces Writer's Bump: Changing Times, Changing
Common callouses are formed by the accumulation of keratinocytes in the stratum corneum in response to excess pressure or friction. Authors report 2 cases of unusual callous formation and an additional 25 more sequential cases that were due to excessive cell phone grip.

Case 1
A 48-year-old woman reported the development of a rough, slightly painful callous on her right thumb. The condition caused mild social embarrassment when shaking hands and was occasionally painful to touch. She denied any preexisting skin conditions and was unaware of any precipitating causes.

On exam, a scaly, thickened, mildly erythematous, poorly defined plaque or callous was noted extending along her right medial thumb to web space. Observation showed that the plaque corresponded to the position she carried her cell phone and she admitted to constant phone use.

Case 2
A 58-year-old woman reported pain and tenderness over her right medial thumb. Exam showed a thickened, slightly scaly, creased callous extending from the thumb to the palm. She noted symptoms had begun when she started training for a marathon and held her phone tightly in the right hand for several hours at a time. ?

Researchers reported similar thumb callouses from excessive video game playing and cell phone callouses, and blisters have also been previously reported. Two patients presented within a very short time frame with medial thumb callouses due to excessive cell phone gripping. Serial examination of 35 other individuals who were heavy cell phone users (Do you hold your cell phone more than 3 h a day) showed similar bumps in 25 people. “Writer's bump” is a similar condition, which has been observed on the lateral knuckle of the third finger in individuals who tightly gripped pens or pencils. “Writer's bump” or callous is rapidly being replaced by “cell callous” or the term we prefer, “cell thumb.” Treatment would consist of keratolytic creams or repositioning the individual's grip on the phone, or better yet, putting the cell phone down altogether.

Source: https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6984141/