The 12-percent ammonium lactate lotion is a topical treatment for ichthyosis vulgaris, xerosis and other conditions that cause dryness and scaliness of the skin, according to WebMD. The lotion increases moisture in the skin and treats itchiness caused by the skin condition

The ammonium lactate lotion should be applied and rubbed thoroughly into the affected skin twice a day, advises MedicineNet.
The lotion may cause a stinging or burning sensation when applied to skin with abrasions or fissures, warns DailyMed.
Skin treated with ammonium lactate lotion should be protected from exposure to natural or artificial sunlight.

From Wikipedia,
Ammonium lactate

Ammonium lactate Lac-hydrin

Ammonium lactate is a compound with formula NH4(C2H4(OH)COO). It is the ammonium salt of lactic acid. Has mild anti-bacterial properties.

the active ingredient of the skin lotions Amlactin and Lac-Hydrin.[1]

Ammonium lactate is a mix of lactic acid and ammonium hydroxide.
It is used as a skin moisturizer lotion to treat dry, scaly, itchy skin.
Those who are using it should avoid exposure to sunlight or artificial UV rays, such as sunlamps or tanning beds.
Ammonium lactate makes skin more sensitive to sunlight.
Skin is more likely to sunburn. Use sunblock and wear clothes when exposed to sunlight