I have a dry patch in corner of mouth, it looks lije fever blister, what can I do to heal it?

Perleche. Often dry, red or cracked rashes in the corner of the mouth are caused by a yeast infection and is known as perleche. Over-the-counter anti-fungal creams can often help. Fever blisters can occur in the corner of the mouth as well, but are treated with prescription anti-viral medicines.