Man Lā Yaḥḍuruh al-Faqīh
Hadith 11332701 - وَ فِي خَبَرٍ آخَرَ : «مُدّاً مِنْ طَعَامٍ أَوْ كَفَّيْنِ».
والأولى أن لا يحك المحرم رأسه إلا حكا رفيقا بأطراف الأصابع.
Hadith.2701 - In another narration: "A mudd of food or two handfuls."
It is preferable that the person in the state of ihram does not scratch their head except gently, using the tips of their fingers.