Can You Make Wudu with Sunblock On?
Question

I got a job a month ago, and I used to use sunblock because of my work situation, and when the time for prayer came, I would do Wudu and pray. Then I read that sunblock may prevent water from reaching the skin when doing Wudu, and most of the time I was using sunblock. My question is: what must I do now? Do I have to repeat my prayers? Please note that it is very difficult for me to work out the number of prayers I must make up, except the prayers of today only, because I am certain that I put on sunblock today when I did Wudu?
Praise be to Allah.The Importance of Water Reaching the Skin in Wudu
It is obligatory to remove anything that may prevent water from reaching the skin, so that you will be able to wash the parts of the body in Wudu as enjoined in the verse in which Allah, may He be Exalted, says (interpretation of the meaning):
{O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles.} [Al-Ma’idah 5:6]
The Prophet (blessings and peace of Allah be upon him) said to Abu Dharr (may Allah be pleased with him): “If you find water and make it touch your skin, that is good.” (Narrated by Abu Dawud, 332; classed as authentic by Al-Albani in Sahih Abu Dawud)
What prevents water from reaching the skin is that which has a substance and thickness, and does not dissolve in water.
As for that which has no substance, and only leaves its colour or a greasy trace, like olive oil and the like, there is no need to remove it.
An-Nawawi (may Allah have mercy on him) said in Al-Majmu` (1/456): If there is some wax, dough, henna or the like on one of his limbs, and it prevents water from reaching any part of that limb, then his Wudu is not valid, whether it is on most of the limb or only on a small area. If what remains on his hand or other limb is a trace and the colour of henna, not its substance, or a trace of liquid grease, such that water still touches the skin of that limb and runs over it, but does not remain there, then his Wudu is valid. (End quote)
Ibn Shata Al-Bakri (may Allah have mercy on him) said:
Traces of ink and henna do not matter. What is meant by traces is mere colour, such that if you scratch it, for example, nothing comes off.” (End quote from I`anat At-Talibin, 1/35)
Shaykh Ibn Baz (may Allah have mercy on him) was asked: If there is a layer of a greasy substance, specifically Vaseline, does it prevent the water from reaching the skin? What must a person do if he did Wudu and prayed many prayers with this, when it was still on his hand, without him realising that the grease prevents water from reaching the skin? How can he get rid of this greasy substance?
He replied: Lotions that have no substance do not prevent water from reaching the skin, whether they come in the form of oil or grease or some other type of lotion that has no substance. They do not prevent water from reaching the skin.
But if it is something that has substance and leaves a trace that prevents water from reaching the skin, then you should remove it; whether it is on your hand, your face or your foot, you should remove it. If you rub your hand or face or foot with something that has no substance and nothing is left of it – rather it only leaves a trace of which you feel some sensation and the like – this does not prevent the water from reaching the skin and there is nothing wrong with that. What prevents water from reaching the skin is that which has a substance that forms a barrier between the water and the skin.” (End quote from Fatawa Ibn Baz,  5/245).
Does Sunblock Prevent Water from Reaching the Skin?
Based on that, if the sunblock has substance and does not dissolve in water, then Wudu and Ghusl done with it on the skin are not valid, and you must repeat the prayers that you offered after you did Wudu having put sunblock on your skin.
You should try to work out the number of these prayers, and try to err on the side of caution so as to absolve yourself.
But if the sunblock did not have any substance, or it had substance but it dissolved when water touched the skin, then it does not matter if you were wearing it.
For more details, please see the following answers: 88179, 85031.
And Allah knows best.