Is it permissible for women to trim hair to take out louse?
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
In principle, it is not permissible for women to cut or trim their head hair.
Therefore, first make Dua to Allah that He removes the lice from the hair.
Thereafter, consult with experts and use the recommended medication etc. to remove the lice from the hair.
If after adopting all possible means, the lice still remain, and it is hoped that trimming the hair will help remove the lice, then it is permissible to trim the hair only to the extent of necessity.
And Allah Ta’āla Knows Best
(Mufti) Abdul Azeem bin Abdur Rahman
Checked and Approved by,
My Esteemed Ustadh Mufti Husain Kadodia Saheb Damat Barakatuhum
The Shar’a ruling herein given is based specifically on the question posed and should be read in conjunction with the question.
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 الضَّرُورَاتُ تُبِيحُ الْمَحْظُورَاتِ.(مجلة الأحكام العدلية، المادة 21)
مَا أُبِيحَ لِلضَّرُورَةِ يَتَقَدَّرُ بِقَدْرِهَا. (مجلة الأحكام العدلية، المادة 22)