It sounds uncomfortable and concerning to have sudden itching with redness spreading to your legs. This could be an allergic reaction that may need prompt attention.

• You can take an oral antihistamine like levocetirizine (found in Xyzal Tablet) to help reduce itching and redness, but only if you have no known allergies to it and no contraindications.
• Avoid scratching the affected areas to prevent skin damage or infection.
• Apply a cool compress to soothe the skin.
• If you notice swelling of the face, lips, difficulty breathing, or the rash spreading rapidly, seek emergency care immediately by calling Apollo Emergency at 1066.
• It is important to consult a dermatologist or allergist promptly to identify the cause and get appropriate treatment.

If you want, I can explain how antihistamines work or suggest home care tips for allergic skin reactions.To narrow down potential causes, we will need some more information.Please tell me your age and gender.