This study contributes to the understanding of how behavioral nudges in email marketing campaigns’ subject lines influence the email open rates and also add to research about fear of missing out in email marketing. We performed field experiments randomly assigned to subscribers by the email marketing software with different versions of the subject line to explore which one resulted in a higher open rate. Email campaigns for hair products were sent using Mailchimp’s A/B testing from December 2023 to February 2024. We chose the hair cosmetics industry because of the steady increase in demand during the past years. Results show that the presence of FoMO nudges in the subject line of email campaigns has a positive effect on open rates when the FoMO appeal is based on scarcity and is subtle. The mere presence of a FoMO “don’t miss out” text is not effective in increasing email open rates.