Why has my mosquito bite turned purple?

Scratching?: Excessive scratching or rubbing can cause a mosquito bite to discolor further and look worse than it is. Try using an over the counter Hydrocortisone or anti-itch preparation. Also, ice packs are great for calming itch without causing the damage your fingernails cause. If the bite continues to be a problem, see your dermatologist to be sure that it is, in fact, a bite.

Anticoagulant: Mosquitoes have an anticoagulant in their saliva, so bruising is common. Get help if there are signs of infection. Signs of infection can include: increased swelling, redness, tenderness, ^ pain, warmth, red streaks, purulent drainage, swollen lymph nodes or fever.

Mosquito bite: Turning purple, shouldn't worry you, unless, painfull, or started to be inflamed , just keep the area clean, you can apply OTC hydrocortisone 1% cream twice a day for few days, good luck