salaam,

"Women must uncover their faces and hands when they enter ihraam for Hajj or ‘Umrah. At this time, they are forbidden to wear niqaab and gloves, because the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The woman who is in ihraam must not wear niqaab or gloves.”

If a woman needs to cover her face because men are passing close by her, or she is beautiful and is sure that men are looking at her, she should drop a part of head covering over her face, because of the hadeeth of ‘Aa’ishah in which she said, “Riders were passing by us, and we were in ihraam with the Messenger of Allaah (peace and blessings of Allaah be upon him), so when they came near, each of us would lower her jilbaab over her face, and when they went away we would uncover our faces again.”

and this is a story which my mum told me....lol

Naz's mum : a husband had gone to Hajj with his wife....and as other women had done his wife had worn the full niqaab. the husband grabbed another woman by the arm thinking it was his wife...but it wasnt her. so thats one of the reasons why you dont wear the niqaab for that prescribed time inshAllah.

but Allahu Alam about that ^^^^

wassalam