These verbs all have the same meaning. The difference is in their grammatical structure:

LET + PERSON/THING + VERB (base form - without "to")

Examples:

I don't let my kids watch violent movies.

Mary's father won't let her adopt a puppy because he's allergic to dogs.

Our boss doesn't let us eat lunch at our desks; we have to eat in the cafeteria.

Oops! I wasn't paying attention while cooking, and I let the food burn.

Don't let the advertising expenses surpass $1000.

The simple past tense of let is also let; there is no change!

The verbs allow and permit are more formal ways to say "let." However, with allow and permit, we use to + verb:

I don't allow my kids to watch violent movies.

Our boss doesn't permit us to eat lunch at our desks.

Permit is the most formal, let is the least formal, and allow is in the middle.

With permit and allow, we can also say that something is or is not permitted/allowed:

Smoking is not allowed.

Employees are allowed to take a one-hour lunch break.

Passengers are not permitted to use cell phones during takeoff.

With a tourist visa, you are permitted to stay in the country for 90 days.

Benefits of Oranges

Prevents hair loss

Orange has high Vitamin C content which is required for producing collagen which, in turn, is responsible for keeping the tissues in your hair together. Nobody likes bald patches on their head, and eating oranges can ensure that you do not have to part with your lovely hair as you grow older.