Confusion lies in the use of the word humidity. Someone somewhere read that cyanoacrylate lash adhesives needs to be 40-70% relative humidity and that is confused with actual humidity. Lash adhesives need to be in 40-70% relative humidity not actual humidity. Cyanoacrylate, the main ingredient in all lash adhesives, is sensitive to relative humidity, not actual humidity. Relative humidity is the measurement of the amount of moisture present, to the ratio of moisture that temperature air can hold.
For relative humidity to be outside the 40-70% range we would be physically uncomfortable and would put on the heater or air conditioner. For example, for relative humidity to be lower than 40% you would realistically need to be in a room that is hotter than 90 degrees and in relative humidity of 70% you and your client will likely to be sweating.
You can be in a place that is 20% humidity outside up to 90% so relative humidity of 40-70% not actual is a perfect level for lash adhesives. Too much moisture in the air can cause shock polymerization, resulting in a week bond and too little can result in the adhesive to be slow and taking forever to bond. The truth is that actual humidity levels are very rarely an issue at all when performing lash services in a climate-controlled setting. If you are having issues with dry time and retention it is more likely that; the adhesive is poor quality, out of date, applied too thick or incorrect application.