Here's another reference for allergic reactions to lactose:

Allergic skin reactivity and chemical properties of allergens in two 
grades of lactose.
Author(s): Kaminogawa, S, Kumagai, Y, Yamauchi, K, Iwasaki, E, 
Mukoyama, T, Baba, M
Source: Journal of Food Science Volume: 49 Issue: 2 Pages: 529-530, 
535 Published: 1984

Abstract: Skin tests of the nondialysable fraction of lactose were 
performed on patients with a clinical diagnosis of cow's milk 
allergy. Yields of brownish-coloured residue allergens (ALG), were 
0.006% from reagent grade lactose (ALG 1) and 0.011% from lactose 
used in a commercial infant food formula (ALG 2). The ALG was 
separated into 4 fractions by chromatography on Sephadex G-75. 
Highest incidences of positive skin reaction among the 4 ALG 1 and 
ALG 2 fractions were 8/9 and 8/12 resp. ALG fractions were identified 
as a sugar protein complex and the protein moiety of ALG contained 
high amounts of glutamic acid (or glutamine), threonine, asparagic 
acid (or asparagine) and proline.
Accession Number: 1984-09-L?0649
Document Type: Journal Article
Language of Text: English
Address: Dep. of Agric. Chem., Univ. of Tokyo, 1-1-1 Yayoi, 
Bunkyo-ku, Tokyo 113, Japan
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See full article (may need to register)
http://www.blackwell-synergy.com/loi/jfds
I have been able to obtain the .pdf if anyone is interested