Is it permissible for him to remove his body hair with a laser? Will that affect his fast?

Praise be to Allah

Whatever the Lawgiver has instructed us to leave alone of hair on the
body, such as the beard and eyebrows, nothing should be removed from them,
whether that is done whilst fasting or at any other time. 

What we have been commanded to remove, may be removed as much as indicated
by Islamic teaching, such as the armpit hair, pubic hair, and the moustache
in the case of men. 

Whatever has not been mentioned in the teachings is pardoned. That includes
hair of the nose, chest, back, legs and forearms. 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 

Removal of hair may be divided into several categories: 

1.

Hair which the Lawgiver has commanded us to remove, such as pubic hair,
armpit hair and the moustache which we are commanded to trim.

2.

Hair which the Lawgiver has forbidden us to remove: the hair of the beard.
Plucking the eyebrows is also prohibited. 

3.

Hair concerning which the Lawgiver has not said anything, such as hair on
the head, legs, arms and the rest of the body. With regard to that
concerning which the Lawgiver has not said anything, some of the scholars
stated that it is not allowed to remove it, because removing it is changing
the creation of Allah, and changing the creation of Allah is something that
is enjoined by the Shaytaan, because Allah, may He be exalted, tells us that
he said (interpretation of the meaning): “and
indeed I will order them to change the nature created by Allah”
[an-Nisa’ 4:119].  Other
scholars said that it is permissible to remove it, because nothing was said
about it; sharee‘ah commands, prohibits and stays silent, and when it has
stayed silent and said nothing, it is known that this is something that is
neither enjoined nor prohibited, because if it was prohibited, sharee‘ah
would have prohibited it, and if it was enjoined, it would have enjoined
it. 

The latter view is more likely to be correct, in terms of argument, because
removing hair that it is not forbidden to remove is permissible.

End quote from Majmoo‘ Fataawa wa Rasaa’il al-‘Uthaymeen
(11/205-206) 

Please see also the answer to question no. 45557

Conclusion: with regard to removing hair from the body, what matters is
whether the Lawgiver has given permission to remove it. 

After that, it makes no difference whether it is done by laser or any other
means of removing it. 

The basic principle is that it is permissible to use a laser for that and
for other permissible uses, unless trustworthy doctors state that the body
may be harmed by that. In that case it is not permissible to use that which
will cause harm to it. 

Moreover, this matter has nothing to do with the fast at all, because
fasting does not make it allowed or disallowed to remove hair whilst
fasting, and the fast is not invalidated or enhanced by that. It has nothing
to do with it. 

But if a person removes any of his hair by way of sin and disobedience, then
doing so in Ramadan is worse, because he should guard against sin and
disobedience before he fasts by refraining from food, drink and physical
pleasures. 

Please see also the answer to question no.
14030 

And Allah knows best.