The ichthyoses include a variety of diseases and consequently treatments vary considerably.
For the inherited ichthyoses, the mainstays of therapy often include emollients or topical keratolytics. Topical and systemic retinoids can be helpful in reducing scaling.
Treatment of acquired ichthyosis focuses on symptomatic management, combined with cessation and/or substitution of any medications that may be causing the condition, or optimization of management of any underlying conditions. Symptomatic management includes emollients alone or emollients with humectants and/or keratolytics.
Of note, the therapies addressed below relate to the more common ichthyoses that do not have significant systemic involvement. The syndromic ichthyoses vary considerably in their underlying defect, and a detailed review of therapy for each of these conditions is beyond the scope of this review.
The taut, cellophane-like membrane that may cover newborns with autosomal recessive congenital ichthyosis can be managed with conservative measures, including aggressive hydration with a humidified chamber and topical lubrication with petrolatum.  Close monitoring for infection and electrolyte disturbances is also important.
The 2 common primary ichthyoses are ichthyosis vulgaris and X-linked ichthyosis. The severity of disease in these 2 groups of patients tends to be milder compared with the other ichthyoses.
Treatment is directed at increasing the hydration of the epidermis. This is achieved through increasing the water content of skin through bathing and increasing ambient humidity, and maintaining this increased hydration through regular application of emollients.  
Plain petrolatum works well as an emollient. The addition of humectants (hygroscopic compounds) to preparations can be used to increase the water-binding capacity of the skin. Common humectants include urea and ammonium lactate.
Scaling can be addressed with the application of preparations that contain alpha- and beta-hydroxy acids (e.g., glycolic acid or salicylic acid), which act as keratolytic agents to break down the scales.  
The scaling that is present in lamellar ichthyosis is usually much thicker than that found in the more common primary ichthyoses and may warrant more aggressive therapy.
In addition to the use of straightforward emollients such as petrolatum, lamellar ichthyosis may benefit from the addition of specially formulated topical preparations that combine keratolytics with humectants.  Topical retinoids have also been reported as effective for the treatment of lamellar ichthyosis and can be used in addition to the previously mentioned therapies.  Because irritation is a common adverse effect, topical retinoids are usually only considered as adjunct therapy if moisturizers, humectants, and keratolytics alone are unsuccessful at controlling disease.
Oral retinoids are a very effective second-line treatment for lamellar ichthyosis, and have a long-term adverse-effect profile that is relatively well defined and safe with appropriate monitoring.  This involves regular laboratory evaluation to monitor fasting lipids and liver enzymes. 
First-line therapies for milder disease presenting with fine scaling without significant irritation or bacterial overgrowth include emollients alone; keratolytics and humectants may be added if topical emollients alone do not control disease.  
Systemic retinoids can be used as a second-line option, but must be initiated at low doses with weekly clinical monitoring, as blistering can occur initially in some cases.   If treatment with isotretinoin is being considered as long-term therapy, patients should engage with the iPLEDGE program.
Compared with the other ichthyoses, the spinous hyperkeratosis and scales of patients with epidermolytic ichthyosis tend to be more prone to bacterial overgrowth and its consequent malodor. Decreasing the bacterial counts with dilute bleach bath (1 quarter cup in a full bathtub) and antibacterial soaps and topical antibiotics (mupirocin) can help reduce the bacterial colonization of the skin. Masking the odor can also be accomplished through perfumes and deodorants. 
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