Things to Avoid in Ihram
Question

What are the things that the (pilgrim) muhrim must avoid?
Praise be to Allah.Things to avoid in ihram
The things which are forbidden in ihram are things which a person must refrain from doing because of being in ihram. They are: 
1.Shaving the hair of the head, because Allah says (interpretation of the meaning): 
“and do not shave your heads until the Hady [sacrificial animal] reaches the place of sacrifice.” [al-Baqarah 2:196]
The scholars added to the prohibition on shaving the head, the prohibition on shaving any hair on the body, and on `. 
2.Using perfume after entering ihram , whether on one’s clothes or body, or in one's food or when washing the deceased muhrim or in any way whatsoever. Using perfume is forbidden in ihram because the Prophet (peace and blessings of Allah be upon him) said concerning a man whose camel trampled him to death, “Wash him with water and lotus leaves and shroud him in his two garments, but do not cover his head or perfume him with hanut.” Hanut is a mixture of perfumes that is usually applied to the deceased. 
3.Intercourse, because Allah says (interpretation of the meaning):
“So whosoever intends to perform Hajj therein (by assuming Ihram), then he should not have sexual relations (with his wife), nor commit sin, nor dispute unjustly during the Hajj.” [al-Baqarah 2:197] 
4.Touching one’s wife with desire , because this comes under the general meaning of the phrase “he should not have sexual relations (with his wife)”, and because it is not permissible for the muhrim (person in ihram) to get married or to propose marriage – so it is more likely that it is not permissible for him to touch his wife with desire. 
5.Killing game (hunting), because Allah says (interpretation of the meaning: 
“O you who believe! Kill not the game while you are in a state of Ihram [for Hajj or ‘Umrah (pilgrimage)].” [al-Maidah 5:95]
As for cutting down the trees, that is not haram for the muhrim, except for those trees within the amyal, i.e., the boundaries of the sanctuary, cutting which is forbidden whether one is in ihram or not. Hence it is permissible to cut down trees in ‘Arafah even if one is in ihram, because the prohibition on cutting down trees is connected to the Haram (sanctuary), not ihram. 
6. A prohibition which applies exclusively to men is wearing shirts, hooded robes, trousers, turbans and leather slippers, because the Prophet (peace and blessings of Allah be upon him) was asked about what the muhrim should wear. He said: “He should not wear a shirt, hooded robe (burnus), trousers, a turban or leather slippers.” But he (peace and blessings of Allah be upon him) made an exception for one who cannot find an izar (lower garment or waist wrapper), who may wear trousers, and one who cannot find sandals, who may wear leather slippers. 
These five things are described by the scholars as wearing sewn garments , so the common folk imagine that wearing sewn garments means wearing clothes that have stitching in them, but that is not the case. What the scholars meant by that is wearing clothes that are tailored to fit the body or part of it, such as shirts and trousers. This is what they meant. Hence if a person wears a rida (upper garment) or izar (lower garment) with patches on it, that is o.k., but if he wears a woven shirt with no stitching, that is haram. 
7. One of the prohibitions of ihram that applies only to women is niqab , which refers to a veil that covers the face and leaves the eyes uncovered, because the Prophet (peace and blessings of Allah be upon him) forbade that. A similar prohibition applies to the burqa’. When a woman enters ihram, she should not wear a niqab or burqa’ . It is prescribed for her to leave her face uncovered except when a non-mahram man passes by her, when she must cover her face and it does not matter if this cover touches her face. 
Expiation for breaking ihram rules
With regard to the one who does any of these forbidden things out of forgetfulness or ignorance or because he is forced to do so, he does not have to offer any expiation, because Allah says: 
“And there is no sin on you concerning that in which you made a mistake except in regard to what your hearts deliberately intend.” [al-Ahzab 33:5]
And Allah says concerning killing game or hunting, which is one of the things that are forbidden in ihram (interpretation of the meaning): 
“O you who believe! Kill not the game while you are in a state of Ihram [for Hajj or ‘Umrah (pilgrimage)], and whosoever of you kills it intentionally, the penalty is an offering, brought to the Ka‘bah, of an eatable animal (i.e. sheep, goat, cow) equivalent to the one he killed.” [al-Maidah 5:95]
These texts indicate that whoever does one of the prohibited actions out of forgetfulness or ignorance does not have to offer any expiation. 
The same applies if he is forced to do it, because Allah says (interpretation of the meaning): 
“Whoever disbelieved in Allah after his belief, except him who is forced thereto and whose heart is at rest with Faith; but such as open their breasts to disbelief, on them is wrath from Allah, and theirs will be a great torment”[al-Nahl 16:106]
If that is what is said about being forced into disbelief, it is more likely that no expiation would be required concerning less serious matters. 
But if the person who forgot remembers, he has to stop doing the forbidden thing, and if one who was ignorant of it comes to know, he has to stop doing the forbidden thing, and if the pressure is lifted from the one from who is being forced, he has to stop doing the forbidden thing. 
For example, if a muhrim covers his head because he forgot, then he remembers, then he has to remove the cover, and if he washes his hand with perfume then he remembers, he has to wash it until the perfume is removed, and so on. 
And Allah knows best.