Comment
Consistent with our hypothesis, changes to the fifth digit were prevalent in the surveyed population, with 85 (22.7%) respondents admitting to changes to their fifth digit from holding a smartphone. The changes to the fifth digit were described as 1 or more of the following: divot (impression), callus (skin thickening), bruise, wound, misalignment, or bending. Most respondents who noted skin changes on the survey endorsed changes consistent with calluses and/or divots. These changes can be described as scaly, lichenified, well-demarcated papules or plaques with variable overlying hyperpigmentation and surrounding erythema. In cases with resulting chronic indentations of the skin, one also would observe localized sclerosis, atrophy, and/or induration of the area, which we found to be less prevalent than expected considering the popularity and notable reliance on smartphones.2
The most commonly reported chronic skin changes to the fifth digit are similar to those of lichen simplex chronicus and/or exogenous lobular panniculitis, which can be both symptomatically and cosmetically troubling for a patient. Functional impairment in movement of the fifth digit may result from the overlying lichenification and induration, as well as from lipoatrophy of the underlying traumatized subcutaneous fat, especially if the affected area is overlying the proximal interphalangeal joint of the fifth digit. These resulting alterations in the skin of the fifth digit also may be cosmetically displeasing to the patient.
On histology, we would expect similar changes to that of lichen simplex chronicus—compact hyperkeratosis and hypergranulosis—and/or an exogenous lobular panniculitis. Lobular panniculitis demonstrates necrosis of the fat lobule; vacuolated spaces; and lipomembranous changes such as fatty cystic degeneration with feathery eosinophilic material in an arabesque pattern, which has been described as frost on a windowpane, or a ferning pattern at the edge of the lipid vacuole.10
We also were correct in our hypothesis that prevalence of changes to the fifth digit correlate with amount of time spent on smartphones per day. Bivariate and multivariate logistic regression analysis showed that a change to the fifth digit was not significantly associated with hand dominance or socioeconomic factors (ie, age, sex, legal marital status, ethnicity, race, annual household income, highest-earned educational degree, current employment status, health insurance status, and state of residence). Controlling for all other factors, the only factor that significantly increased the odds of experiencing a change to the fifth digit was the amount of time spent on the phone per day. The respondents who spent more than 5 hours per day on their phones had 5-times greater odds of experiencing a change to their fifth digit compared with respondents who spent less than 1 hour per day on their phones (P=.045).
Although no other correlations with changes to the fifth digit, such as type of smartphone used, were found in our study, future studies should continue to investigate other potential factors that play a role in smartphone use changing the appearance and function of the digits. Our lack of significant correlations with changes to the fifth digit could be attributed to a small sample size and other possible factors, such as the frequent design changes of smartphones by manufacturers. Our study also is limited by the possibility of other factors contributing to these observed skin changes. Although we have anecdotally observed these skin changes and have hypothesized that smartphones are the culprit, other causes, such as holding certain tools, could lead to these skin changes. In addition, there are many different ways to hold a smartphone, and certain hand positionings may be more or less prone to skin changes described in our study. Various accessories, such as cases and gripping devices, also may change the way smartphones are held and would skew the results of our survey. Future studies could examine different ways smartphones are held, how various accessories affect these skin changes, and the size or model of phones that make these skin changes more or less prevalent.
Conclusion
Our study is an initial step in uncovering a possible phenomenon of smartphone use affecting the digits, namely the fifth digit. Our findings demonstrate that the amount of time spent on the phone per day significantly increases the odds of experiencing a change to the fifth digit. We expect these potential skin changes as well as other musculoskeletal changes to increase in prevalence as daily smartphone use continues to increase. With the lack of studies investigating skin changes to the digits in relation to smartphone use, future studies are needed to verify our results and confirm the presence of this issue.