Can I wash my hair after an hour of application of Minoxidil 5%?

I would try to leave the monoxidal foam on your scalp overnight. If possible for at least eight hours, there seems to be studies supporting this that it will have better results if done 8 hours. But can't have some benefit, even with the four hours. 1ml is fine use.Side effects can include Unwanted hair growth, if the cream is applied in areas that it should not go. There seems to be a very small percentage of people who claim they get palpitations and headaches specifically women. Speak to your doctor thank you for the question

Hello, Dr. George Abrahamian here from LA FUE Hair Clinic in Pasadena, CA. It is advisable to leave minoxidil on the scalp for it to be effective. If you are planning on washing your hair, wash the hair first, towel dry your head, and apply the minoxidil to the scalp after the fact. It is okay if the hair/scalp is a bit damp, this can act as a vehicle to get the minoxidil to the scalp easier, but you dont want the hair/head to be overtly wet during application.
The most common side effects of minoxidil include dry, red, itchy and flaky skin on the scalp, which usually resolves as your scalp gets used to the minoxidil. There are some reports of heart palpitations, dark circles under the eyes with minoxidil use, but these are very rare, and typically occur in women, or people who are hypersensitive to minoxidil use.
I hope this helps.

How long should minoxidil be left on the scalp? Minoxidil needs to be left on the scalp at least 4 hours and 8 hours (or longer) is much better. The recommended dose is 1 mL of the solution twice daily or one half of the cap for the foam (either once daily for women or twice daily for men).
This recommendation I give comes from a study done in 1990. In this research study, twenty-two male study participants  completed a four-way, multiple-dose, randomized crossover study to investigate  the relationship between how long the drug was applied to the scalp and the amount of minoxidil absorption. A 2% topical solution was used in the studies.  The researchers comparedhow 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.
Conclusion:
Although minoxidil should ideally be left on 8 hours, a significang amount of benefit can still be achieved with 4 hour use. Even at 1 hour about one half is absorbed but clearly this is less than ideal. Understanding the absorption of minoxidil is important to help improve the ability of patients to 'stick with' the treatment. 
 
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