Question Summary:
while performing ghusl you have to wash your hair throughly. But she has a skin disease on her head, psoriasias. The doctor recommended a special shampoo and medication for it.must she still wash her hair of is she allowed to just wash her body?

Question Detail:

I know that you have to perform ghusl after having intimacy.

Now she has the following problem: while performing ghusl you have to wash your hair throughly. But she has a skin disease on her head, psoriasias. The doctor recommended a special shampoo and medication for it. When she uses the shampoo and medication, she doesn't suffer from the disease. But the doctor told her she cant use the shampoo on a daily base because the medication and shampoo is too strong and it will damage her hair, skin and can cause hair loss. If she doesnt use it frequently, the disease will come back. When she washes her hair without the shampoo and medication, the disease starts returning within a few days.
Now the question is: must she still wash her hair of is she allowed to just wash her body?  

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatuh
If one has a certain disease or condition which does not permit the use of water on the affected area due to the further harms or complications it may cause, then it is permissible for them to abstain from the use of water if advised to do so by a physician. If washing the affected area with water will cause harm, she should make masah (wipe over the area with a wet hand) over the head. If that too will cause harm, then it is permissible to leave the affected area unwashed until she uses the shampoo to treat the scalp.
 
و ذكر شمس الائمة الحلواني اذا كان في اعضائه شقاق و قد عجز عن غسله سقط عنه قرض الغسل و يلزم امرار الماء عليه فان عجز عن امرار الماء  يكفيه المسح فان عجز عن المسح سقط عنه المسح أيضا فيغسل ما حوله و يترك ذلك الموضع كذا في الذخيرة
(Fatawa Alamgiree, 1/5, Rashidiyya)
And Allah knows best
Wassalam
Ml. Asif Umar,
Student Darul Iftaa
Checked and Approved by:
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah