Removing armpit hairs with the help of another person

Firstly: 

Allaah has prescribed for His Prophet (peace and blessings of Allaah be upon him) and his ummah the Sunan al-Fitrah (practices that are in accordance with the natural inclinations of man). These are mentioned in the hadeeth of ‘Aa’ishah (may Allaah be pleased with her), who said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Ten things are part of the fitrah: cutting the moustache, letting the beard grow, using siwaak (tooth-stick), snuffing up water into the nose, cutting the nails, washing the finger-joints, plucking the armpit hairs, shaving the pubes and washing the private parts after relieving oneself.” Zakariya said: Mus’ab said: I have forgotten the tenth but I think it was rinsing the mouth. 

Narrated by Muslim, 261. 

The Prophet (peace and blessings of Allaah be upon him) set a time limit with regard to some of these sunnahs, stating that they should not be left for more than forty days, as narrated in the hadeeth of Anas (may Allaah be pleased with him) who said: A time limit was set for us with regard to cutting the moustache, clipping the nails, plucking the armpit hairs and shaving the pubes – we were not to leave these for more than forty days. 

(Narrated by Muslim, 258) 

Secondly: 

It is not permissible for a man to look at the ‘awrah of another man or for a woman to look at the ‘awrah of another woman. 

It was narrated that Abu Sa’eed al-Khudri said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “No man should look at the ‘awrah of another man and no woman should look at the ‘awrah of another woman. No man should be with another man under one cover and no woman should be with another woman under one cover.” 

Narrated by Muslim, 338. 

Al-Nawawi said: 

This indicates that it is haraam for a man to look at the ‘awrah of another man and for a woman to look at the ‘awrah of another woman. There is no dispute among the scholars on this point. Similarly it is haraam, according to scholarly consensus, for a man to look at the ‘awrah of a woman and for a woman to look at the ‘awrah of a man. The Prophet (peace and blessings of Allaah be upon him) warned against a man looking at the ‘awrah of another man and woman looking at the ‘awrah of another woman, and this is more applicable in the case of a man looking at the ‘awrah of a woman and vice versa.  

An exception is made in the case of a married couple, each of whom may look at the ‘awrah of the other. In the case of mahrams, it is permissible for them to look at one another from above the navel and below the knee. All that we have said about looking being forbidden applies when there is no need to do so, and what we have said about it being permissible (among mahrams) applies when there is no desire involved. 

See Fath al-Baari, 9/339 

Thirdly: 

It is permissible for a woman to remove the armpit hair of another woman, because the armpit of a woman is not ‘awrah to another woman, so long as there is no risk of fitnah and so long as there is the certainty that she will not describe the body of the woman she has seen to her husband or any other man or to any other woman.  

See Tafseer Ibn Katheer, 3/258. 

Fourthly: 

With regard to using wax instead of plucking, this is permissible, The Standing Committee was asked: is it permissible for a man to use wax to remove hair such as armpit and pubic hair? 

They replied: 

Yes, it is permissible to use that to remove armpit and pubic hair. 

Fatawa al-Lajnah al-Daa’imah, 5/171 

And Allaah knows best.