Should I bother applying minoxidil if I am going swimming in a few hours?

The Timing of Minoxidil Application: 8 hours Ideal but 1 hour Still May Do Something

Summer months are a great time for swimming. I am often asked if applying minoxidil makes any sense if a person plans to dunk in the pool within a few hours. This is particularly relevant for patients who apply their minoxidil in the morning and plan to swim later that morning or afternoon.

That answer is yes. 

In a 1990 study, twenty-two healthy male volunteers completed a four-way, multiple-dose, randomized crossover study to determine the relationship between contact time of applied drug on the scalp and minoxidil absorption from a 2% topical solution. The researchers examined how much minoxidil is absorbed at 1 hr, 4 hr compared to 11.5 hours. Relative to the amount absorbed after a contact time of 11.5 h, absorption was approximately 50% complete by 1 h and greater than 75% complete by 4 h.

Although minoxidil should ideally be left on 8 hours for “maximal” benefit, tremendous benefit can still be achieved with shorter times - even 1 hour. Understanding the absorption of minoxidil is important to help improve the ability of patients to 'stick with' the treatment. 

Provided a person isn’t going swimming in less than one hour, sticking with one’s normal routine of minoxidil application is advisable.

Of course, the goal is to get maximal absorption wherever possible. For patients who are swimming frequently in the summer, application at night will be important so that the minoxidil has the chance to have at least 8 hours on the scalp. If a morning application is required, even short application times are better than not applying it at all.


Reference

Ferry JJ et al. Relationship between contact time of applied dose and percutaneous absorption of minoxidil from a topical solution. J Pharm Sci. 1990 Jun;79(6):483-6.