Everything Is Permissible in Islam Until Proven Prohibited
Question

I am living here in the West. I was wondering what is the extent that [something is pure until proven that it is prohibited] with respect to food, clothing and soap?
To explain my question further, say I am wanting to buy some food in the supermarket, upon looking at the ingredients, I find that the ingredients are sometimes not fully detailed, such as "spices", and sometimes have ingredients that I don’t know about. Sometimes the food does not label the item as vegetarian or Halal (permissible to eat). This is similar to my situation with the material of clothes and soap, I do not know the origins of some of their materials.
So I am wondering, What is the extent to which I need to investigate such perishables before I can use them? And when should I start relying on the principle that [something is pure until proven that it is prohibited]?
Praise be to Allah.Everything Is Permissible in Islam Until Proven Prohibited
The scholars set a rule that says that in principle everything is permissible, and they based this rule on Shar`i evidence.
Shaykh Al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
“It should be understood that in principle all things, of various types and categories, are generally permissible for human beings, and that they are pure and it is not forbidden for people to handle them and touch them. This is a comprehensive rule that is general in application, and it is an important ruling that is of immense benefit and brings much blessing, and the scholars turned to it when issuing ruling on innumerable actions and issues faced by people. It is based on ten points of evidence – from what I can call to mind of sources of shari‘ah – namely: the Book of Allah, the Sunnah of His Messenger, and following the path of the believers that is mentioned in the verses (interpretation of the meaning): “Obey Allah and obey the Messenger (Muhammad (blessings and peace of Allah be upon him)), and those of you (Muslims) who are in authority” [An-Nisa’ 4:59] and “Verily, your Walee (Protector or Helper) is Allah, His Messenger, and the believers” [Al-Ma’idah 5:55]; in addition to analogy, giving the same rulings to similars situations, rational thinking, and insight.” (Majmu‘ Al-Fatawa, 21/535) 
Then he (may Allah have mercy on him) quoted the evidence for that, so please refer to the book mentioned above.
What this ruling means is that with regard to everything that is of benefit on earth, and what man may attain thereof and make use of, is permissible so long as there is no evidence to indicate that it is prohibited.
Permissible and prohibited food and drinks
With regard to food , drink, clothing and soap (and cleaning materials), this rule is to be followed with regard to everything except in the presence of Shar`i text that gives a ruling about a certain matter or situation, with the exception of the following:

Things containing any considerably harmful ingredients, because the basic principle with regard to harmful substances is that they are prohibited, and they are not included in the rule that says: “in principle everything is permissible”.

Allah, may He be exalted, says (interpretation of the meaning):
“and do not throw yourselves into destruction.” [Al-Baqarah 2:195]
“And do not kill yourselves (nor kill one another). Surely, Allah is Most Merciful to you.” [An-Nisa’ 4:29]
Abu Sa‘id Al-Khudri (may Allah be pleased with him) narrated that the Prophet (blessings and peace of Allah be upon him) said: “There should be neither harming nor reciprocating harm.” Narrated by Al-Hakim (2/57-58). He said: Its chain of narrators is authentic according to the conditions of Muslim. It was also classed as authentic by Al-Albaani in Silsilat Al-Ahaadeeth As-Saheehah (1/498)
Shaykh Muhammad Al-Amin Ash-Shanqiti (may Allah have mercy on him) discussed this issue and said:
“If it is purely harmful with no benefit at all, then it is prohibited, because the Prophet (blessings and peace of Allah be upon him) said: “There should be neither harming nor reciprocating harm.”
If it is beneficial in some ways and harmful in others, then one of three scenarios must apply:

Either the benefit outweighs the harm
or the converse is true
or the benefit and harm are equal.

If the harm outweighs the benefit or is equal to it, then it is not allowed, because of the Hadith, “There should be neither harming nor reciprocating harm,” and because warding off harm takes precedence over achieving interests.
If the benefit outweighs the harm, then the most correct view is that it is permissible, because it is a well-established principle that greater benefits take precedence over lesser harms.” (Adwa’ Al-Bayan, 7/793-794)

The basic principle with regard to meat is that it is prohibited.

That is because it is not permissible to eat meat unless it is slaughtered in the proper (Islamic) manner, fulfilling all the necessary conditions.
Al-Khataabi (may Allah have mercy on him) said:
“With regard to anything that is prohibited in principle, it only becomes permissible if it fulfils the necessary conditions and is done in the proper manner, such as intimate relationships, which do not become permissible until after marriage. 
Similarly, the meat of sheep does not become permissible unless it is slaughtered in the proper manner. If there is any doubt concerning the fulfilment of these conditions, and whether they were met for certain in the manner that indicates that it has become permissible, then the original principle remains in effect and the meat is prohibited.” (Ma‘alim As-Sunan, 3/57)
However, in order to prove that it is permissible, it is sufficient to know that the one who slaughtered it was a Muslim or one of the People of the Book (a Jew or Christian). After that it is not necessary to ascertain the method of slaughter for each animal.
Based on that, with regard to meat that is available in a Muslim or Christian country, it is deemed to be permissible, unless it is proven that it was slaughtered in a way that is contrary to Islamic rulings, such as strangling or electric shock, or that the name of Allah was not mentioned over it, and so on.
With regard to products for which there is no Shar`i evidence that they are prohibited, or the list of ingredients does not include any components that are prohibited or are harmful, then we rule that it is permissible and pure, and that basic principle is not altered for mere doubts or unproven talk.
Yet, if prohibited ingredients are included in some food , is it prohibited to consume it altogether? This is subject to further detailed discussion, as has been explained in fatwa no. 114129 .
To sum up, if the prohibited substance is still present in its original form, then it is prohibited to consume it. However, if it has been transformed into another substance by means of interactions or manufacturing processes, and the first prohibited substance is no longer present in its original form, then the more correct scholarly view is that it is permissible to consume it.
Permissible and prohibited clothing 
With regard to clothing, it comes under the rule that “in principle everything is permissible”. The basic principle concerning it is that it is permissible, except what is excluded by Islamic rulings, such as silk which is prohibited for men, and some animal skins that cannot be purified by means of tanning. 
And Allah knows best.