It’s not a cause for concern, its likely to be due to folliculitis and all you need to do is clean the area with a good antiseptic, avoid bursting it and take antibiotics with anti-inflammatory analgesic (to reduce redness, swelling and pain). If it happens again you should get your blood
sugar levels tested
It can leave a mark, you can talk to your doctor and opt for topical creams to reduce the pigmentation once it heals