The hijab (etc) is immodest

[Leonardo17]

There are many theories on this. My theory is that in a time when there was no sunscreen, no regular cold shower and of course no air-conditioned jeeps to ride through the desert, the hijab, being of black color was simply the ideal dress for a very hot and arid country. Until the 19th century most European farmer women were also wearing dresses covering their heads and their entire bodies. In fact, the more you go north in the Muslim world also, the less Hijab they are wearing.
 
Ancient people did not have the choice of being stupid. Even on religious issue. Just like a hard working European peasant woman had to protect her body from the sun, the wind, insects etc, Arab women who mostly worked in the area of stock farming in the Arabian Peninsula had to protect themselves from the sun. Otherwise they would be dehydrated and they would die.
 
Now taking this and saying “This is our tradition, This is the rule of God…” etc… that’s a whole different issue (and it’s not true).

Just a note sunscreen is actually an ancient concept

Wikipedia:

Early civilizations used a variety of plant products to help protect the skin from sun damage. For example, ancient Greeks used olive oil for this purpose, and ancient Egyptians used extracts of rice, jasmine, and lupine plants whose products are still used in skin care today.[145] Zinc oxide paste has also been popular for skin protection for thousands of years.[146] Among the nomadic sea-going Sama-Bajau people of the Philippines, Malaysia, and Indonesia, a common type of sun protection is a paste called borak or burak, which was made from water weeds, rice and spices. It is used most commonly by women to protect the face and exposed skin areas from the harsh tropical sun at sea.[147] In Myanmar, , a yellow-white cosmetic paste made of ground bark, is traditionally used for sun protection.

)Interesting