Is IPL still effective if the treatments are spread out several months apart?

IPL could absolutely still be effective when treatments are spaced several months apart. When treating freckling with IPL, typically 2-3 sessions will be necessary and ordinarily we would advise spacing anywhere from 2-4 weeks apart. I think the most important thing to note when spacing treatments further apart is that there is the possibility to take a few steps backwards between treatments. For example, treatment 2-3 times spaced 2-3 weeks apart could really get your skin looking clear and even-toned (depending of course on current condition). Spacing treatments further apart means possibly a greater chance of more sun exposure and developing more freckling between treatments that might not have happened if you were able to complete the series closer together. The point here is that you must take extra care to protect your skin from sun exposure between treatments, as well as be very diligent about applying a daily broad-spectrum sun protection.

I have several clients who travel a lot for work or touring and they do get a good result from quarterly sessions of the IPL, Meaning they will do one every 3-4 months. In between as previously noted, it is very important to use a good sunscreen to protect you in between and especially directly before and after each session. 

Yes, IPL treatments are still effective, even when spaced out. As long as you complete your series, and make sure to avoid worsening your hyperpigmentation with sun exposure while in Mexico, you should be fine. Thanks for the great question!