Seasonal and daylight saving time fluctuations in Google searches for scalp seborrheic dermatitis

Scalp seborrheic dermatitis, or dandruff, is thought to worsen during the winter when there is later sunrise and less daylight. This study investigates trends in search engine interest for the term "dandruff" as they relate to changes in daylight, sunrise, and seasonality. We investigated the search interest in several countries of varying latitudes over a five-year period, and we explore the effect of daylight saving time on disease interest within two cities in the United States. We discuss our findings in the context of hormonal changes and skincare/behavior.


INTRODUCTION
Contributing factors to scalp seborrheic dermatitis (dandruff) development are increased sebum, by-products of microorganisms like Malassezia yeasts, and allergic sensitivity. Dandruff is thought to worsen in severity during the winter, 1 when there is later sunrise and less sunlight. We aimed to evaluate potential seasonal fluctuations of search engine interest for "dandruff " and the possible correlation with daylight, sunrise, and DST shifts.

METHODS
We assessed the frequency of search-engine queries for scalp seborrheic dermatitis over five years (2015-2019) to investigate a possible relationship between sunlight and search interest in the United States, Brazil, South Africa, and Colombia. The United States experiences more intense sunlight in June, July, and August; while South Africa and Brazil experience more intense sunlight in December, January, and February. In Colombia, the sunlight intensity is distributed more evenly throughout the year. We selected English-speaking (United States, South Africa) and non-English-speaking countries (Colombia and Brazil). Lay terminology matching the condition and language of each country was used. Google Trends 2 was used to determine the search frequencies (SF) each week relative to the maximum weekly searches each year. Average monthly frequency was taken over five years, and it was used to plot the average relative search interest in a year cycle ( Figure 1). To investigate the specific effects of sunrise in the United States, we compared search trends for New York City (NYC, observes DST) and Phoenix (ST) for the year of 2018 (the most recent year without the effect of COVID-19 pandemic) (Figure 2). In the United States, searches for dandruff were estimated to be one hundred thousand to one million per month.

RESULTS
When evaluating interest as compared to daylight, it spiked in the late winter (low sunlight) of both northern (United States) and southern (Brazil, South Africa) locations (Figure 1). Dandruff interest occurred throughout the year along the equator (Colombia), with a reduced interest in the two Equinoxes (March and September). In the context of sunrise time, searches increased in the winter when sunrise was later in both NYC and Phoenix. However, searches decreased in March in NYC but peaked again in April, after "springing forward" (unexpected increase). In contrast, the peak followed a typical reduction as the winter faded in Phoenix, without a spring peak. The peaks of interest followed the sunrise time pattern (Figure 2), suggesting that luminosity in the morning might be protective for dandruff. factors could also explain these findings, such as reduced hair washing, increased wintertime interest, or increased media advertising during particular seasons. We could not evaluate hair washing behavior or advertisement trends. Nevertheless, we observe a trend with sunrise/daylight and dandruff search interest. This study suggests that further research should be conducted to assess the correlation between sunlight, sunrise, and dandruff. It could open avenues for the development of sunlight-based therapies for dandruff. l

DISCUSSION AND CONCLUSION
During daylight saving, "springing forward" simulates winter mornings, and the interest in dandruff returns to the winter trends. Natural morning light occurs earlier in the summer and later in the winter, which may influence hormone/ androgen levels 3 and contribute to the seasonal variations in dandruff, as increased sebum production can occur via increased androgen levels.
This research has several limitations. Our study measured interest (Google searches), not necessarily disease. Other