Question Summary:
Is it allowed to use shampoos and soaps that have gelatin as an ingredient?

Question Detail:

Assalamualikum, Grlatin is used widely in the production of today's goods. Many are aware as to the forbiddenness of Haraam Gelatin in food products. However, I wish to inquire about the use of Gelatin in products such as Shampoos and the like, where the Gelatin is not consumed but nevertheless used. Please respond quickly. Jazakhallah.

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The shampoos and soaps that are usually made from animal fat undergo a complete transformation. As a result, it is permissible to use them, even if animal by-products are used in their manufacture. [i][ii][iii][iv]
However, if porcine gelatin (i.e. pigs) is indeed present as an end product in the shampoo or soap then it will be impermissible to use. 
On the other hand, if the gelatin is derived from a non-dhabihah bovine source (i.e. cattle), Mufti Taqi Uthmani (may Allah preserve him) has stated in In'am al-Bari that it will be permissible for external use, whether it is derived from the skin or the bones of cattle. 
This is because the bones of a halal animal are pure regardless of the method of slaughtering and the skin (hide) undergoes a purification process equivalent to tanning [dibagha] which renders it pure for external use. [v][vi] 
Mufti Sohail ibn Arif,
Assistant Mufti, Darul Iftaa
Chicago, USA
Checked and Approved by,
Mufti Ebrahim Desai.
و) يطهر (زيت) تنجس (بجعله صابونا) به يفتى للبلوى) [i]
(قوله: ويطهر زيت إلخ) قد ذكر هذه المسألة العلامة قاسم في فتاواه، وكذا ما سيأتي متنا وشرحها من مسائل التطهير بانقلاب العين، وذكر الأدلة على ذلك بما لا مزيد عليه، وحقق ودقق كما هو دأبه - رحمه الله تعالى -، 
فليراجع.
ثم هذه المسألة قد فرعوها على قول محمد بالطهارة بانقلاب العين الذي عليه الفتوى واختاره أكثر المشايخ خلافا لأبي يوسف كما في شرح المنية والفتح وغيرهما. وعبارة المجتبى: جعل الدهن النجس في صابون يفتى بطهارته؛ لأنه تغير والتغير يطهر عند محمد ويفتى به للبلوى. اهـ. وظاهره أن دهن الميتة كذلك لتعبيره بالنجس دون المتنجس إلا أن يقال هو خاص بالنجس؛ لأن العادة في الصابون وضع الزيت دون بقية الأدهان تأمل، ثم رأيت في شرح المنية ما يؤيد الأول حيث قال: وعليه يتفرع ما لو وقع إنسان أو كلب في قدر الصابون فصار صابونا يكون طاهرا لتبدل الحقيقة.
رد المحتار، ١/ ٣١٥ - ٣١٦ 
فتاوى محمودية، ١٦/ ٢٠٥ – ٢٠٦ [ii]
أحسن الفتاوى، ٢/ ٩١ – ٩٢ [iii]
جديد فقهي مسائل، ضميمة ١ ص. ٢٩٧ - ٢٩٨ [iv]
إنعام الباري، ٢/ ٤٠٧ - ٤١٠  [v]
[vi]  Excerpt from Mufti Taqi Uthmani's fatwa on the permissibility of using collagen (derived from cattle) for external use: 
“The first issue is whether it can be held as pure (tahir). After studying the processes it is quite clear that the hides used for production of these casings become pure after passing through the process which includes lime treatment for 4/5 days. The principle of Shariah is that the hide of an animal, even not slaughtered in the Islamic way, is purified by the process of dibagah (tanning)....The second issue is whether it is halal to eat the casing itself. According to the majority view of the Muslim jurists it is not permissible to eat the hide of an un-slaughtered animal even after tanning. However, a large number of Sha'fie jurists as well as a small number of Hanafi jurists have allowed to eat it after tanning. But this minority view could not find favor with the latter day fuqaha who are of the firm opinion that it is not permissible for oral use and therefore the minority view should not be followed.”  Source: http://albalagh.net/qa/0067.shtml  Last accessed: 06/11/2016