White Patches On Body, Increasing, Large Vitiligo Patch. Used Ammonia. What Is The Cause?

I am over 60. I noticed few scattered white patches , size of a sand particle, on both forearms and few,2-3, white patches on other parts of the body . They have been there for many years and don't seem to be on the increase. It is not visible from a distance, but more visible after sun tan ( I have a light brown skin colour and grey hair). I have a family history of vitiligo (49 year old niece). Are these patches likely to merge and become a typical large vitiligo patch? if so , are there any means of stopping this from happening, and is there any treatment that makes it disappear other than cosmetic comoflage. I use chemical hair dye, with and without amonia. I read warning of using chemical hair dyes as it may cause vitiligo,temporary or permanent.,so is that likely to have been the cause or would it make it increase?