Ruling on using food items for personal hygiene purposes
Question

What is the ruling on using cornstarch for cosmetic purposes in some sensitive areas?
Praise be to Allah.The jurists differed concerning the ruling on using food for personal hygiene and the like, and there are two views:
The first view is that it is permissible and allowed, and there is nothing wrong with using some food items and types of food for the purpose of hygiene and the like.
This was stated by the Hanafis and it is mentioned in one report from Imam Malik. It was also the view favoured by Ibn Qudamah among the Hanbalis.
It says in al-Fatawa al-Hindiyyah (5/337) – which is a Hanafi book – that Abu Hanifah (may Allah have mercy on him) did not see anything wrong with cleaning the hands with flour after eating. His two companions, Abu Yusuf and Muhammad ibn al-Hasan, were of the same view.
An-Nafrawi al-Maliki (may Allah have mercy on him) said:
The permissibility of that was narrated from Maalik (may Allah be pleased with him), as he said – regarding Indian pea (chickling vetch, Lathyrus sativus), fava beans (foul) and similar foods –: There is nothing wrong with cleaning one’s hands with them, or scrubbing oneself with them in the bath."(Al-Fawakih ad-Dawani  2/321).
Ibn Qudamah (may Allah have mercy on him) said:
It was said to Abu ‘Abdillah (Imam Ahmad): What do you say about cleaning one’s hands with the residue left in a sieve? He said: There is nothing wrong with it; we do that.
Al-Khattabi quoted as evidence for the permissibility of that the report narrated by Abu Dawud with his isnad from the Messenger of Allah (blessings and peace of Allah be upon him), according to which he instructed a woman to add salt to the water, then wash off menstrual blood with it. Abu Dawud (313); it was classed as da‘if (weak) by al-Albani. Salt is food, and there are similar reports."(Al-Mughni  7/221).
For more information, please see the answers to questions no. 59899 , 84903 , 145307 .
There is nothing wrong with using food items for the purpose of personal hygiene and the like, and that is not regarded as wasting it; rather it is using it for a purpose that is required according to Islamic teachings. Cleaning oneself and making oneself look good are things that are prescribed and encouraged in Islamic teachings.
The second view is that it is disliked to use food items for personal hygiene purposes. This is the official view of the Malikis and Hanbalis, but the Hanbalis limited that disapproval (makruh) to using staple foods, not all types of foods.
Al-Bahuti al-Hanbali (may Allah have mercy on him) said:
It is disliked to clean one’s hands with food if it is a staple food, even if it is flour made from chickpeas, lentils, beans and so on."(Kashshaf al-Qina‘  5/172).
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
They quoted as evidence for it being disliked to clean one’s hands with staple foods the fact that this leads to those foods becoming contaminated with impurities and dirt. That is why it is not allowed, just as it is not allowed to remove impurities using such foods. Salt is not a staple food; rather it is used to improve the flavor of staple foods.
Yes, it is not allowed to for either humans or jinn to clean themselves after relieving themselves using staple foods of humans and animals. Hence the residue left in a sieve should not be used for cleaning oneself after relieving oneself, even though it is permissible to clean one’s hands with it.
But if there is a need to use staple foods, such as tanning with barley flour, or using yoghurt and flour as a remedy for scabies, and the like, then a concession should be granted allowing that…
This is the answer that may be given regarding salt, because it is being used for a need.
Another piece of evidence is the fact that the Prophet (blessings and peace of Allah be upon him) instructed us to lick our fingers and the plate, and to pick up a dropped morsel and remove the dirt from it. All of that is so that no staple food will be wasted, and using it to scrub oneself is not appropriate because something else may be used instead, and it comes under the heading of extravagance, which is the work of the Shaytan. End quote.
I was asked about a similar case – namely cleaning one’s hands with musk – and I said: This is extravagance, unlike following the traces of menstrual blood with a cloth perfumed with musk, because the latter is a tiny amount that is used for a need, but cleaning the hands with musk is too much and is unnecessary. End quote.
Quoted by Ibn Muflih in al-Adab ash-Shar‘iyyah (3/211).
The right thing is not to use food items for personal hygiene and the like, because there are many readily-available things that can be used instead of them, and that is furthest removed from extravagance and luxury.
But if it so happens in some situation that there is nothing available to use for the purpose of personal hygiene except things that are food items, or there is a need for that, then we hope that there will be nothing wrong with using such things in that case, because of need.
And Allah knows best.