Thanks for posting your query.
It could be a harmless pigmentation or something else.
If you have itching it could be fungal infection
If it do not show any symptoms it needs to be examined initially and relevant investigations like biopsy
might be needed to diagnose .
Since there is increase in number i suggest you to consult a Dermatologist
for further investigations and good local examination.
Hope I have answered your query.
Wishing you good health.