Welcome to Healthcaremagic forum,
The condition what you have is known as Prurigo simplex
,where in one gets itchy skin spots on the legs following a mosquito bite. If the itching has stopped and the marks are left behind then you can use hydroquinone
cream (4%) at night or tretinoin
cream (0.05%) at night .
would not have any effect on the marks .It is usually good for face and not for legs.
But you can try lasers on these spots .The best would be Q-Switched Nd:yag laser for the same.Kindly consult a competent dermatologist
who has good experience on lasers.
Hope I've answered your query.
Senior specialist, Dermatology.