Answered by: Maulana Yusuf Khan
Assalamu alaikum, I think I am likely suffering waswas in regards to this issue because I have not fully understood it. I will present some examples in which I am facing doubts and if you could be so kind to explain to me the correct thought process/procedure in such situations.
I am making wudu, I have washed my face, my arms, I then proceed to wipe my head and as I wipe back to the front I feel some bit on my hairline, and then I question as to what this was, whether this was something that blocked water from my face, and I wonder if my wudu is acceptable. What should I have thought/done instead?
I have finished salah and I notice something on my thumb that’s possibly some skin or something on the skin. I don’t investigate further and it’s not there, later on, it could have been a barrier to my skin.
In what situation is something a barrier to skin that requires repetition of wudu? And is things that come from the skin a barrier? Such as dry skin, grease from skin, etc. Please teach me a normal approach to this situation because my mind is defective (as I fall into waswas).
In the name of Allah, the Most Gracious, the Most Merciful
Wasaawis (whispers) and doubts during whudu is a very common issue and it is important to take the correct measures when faced with such a situation.
In regards to doubts, it is best to be very disciplined in your approach to this. The rule is ‘certainty is not overcome by doubt’, this means that if you are certain you did it then any doubt you may have does not affect it. It is important to weigh the likelihood, but it is important to remember many times these doubts are given from shaytaan.
It is necessary to remove anything from the skin that may be a barrier from the water reaching the skin such as dough, paint etc. Furthermore, it is also necessary to wash what is under the barrier after you have removed it. 
When it comes to removing something which may be acting as a barrier, it is vital to take into account one can only do so much for things like grease etc, so you should try to remove it by rubbing it and using hot water [to help remove it] as much as you can so that the water can reach your skin.
Allah does not obligate anyone beyond his capacity. [Surah-al- Baqarah: Verse 286]
After you have tried as much as you can and exhausted your effort to remove it, and you have made utmost effort to reach water to your skin than in that case you have exhausted your effort.
In regards to whispers from Shaytaan, you should seek refuge in Allah SWT from the whispers of shaytaan, and make dua to Allah SWT to ease your affairs. Whilst also, taking into consideration the legal ruling ‘certainty is not overcome by doubt’. Once you have exhausted your effort in making water reach that area and to remove any barriers then you have done all you can.
Only Allah knows best
Written by Maulana Yusuf Khan
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham