An apparatus comprising: a sweat sensing component for measuring a parameter relating to sweat generated by sweat glands of a subject; a sweat transport channel; and a first sweat redirecting component comprising a first responsive material whose form is configured to change in response to a stimulus, so as to redirect sweat and control an amount of sweat able to be transported to the sweat sensing component via the sweat transport channel; wherein the first sweat redirecting component is positioned at an outlet of the sweat transport channel, such that, in a first configuration, the form of the first responsive material is such that the first sweat redirecting component prevents the passage of sweat through the outlet, and directs the passage of sweat to the sweat sensing component; and, in a second configuration, the form of the first responsive material is such that the first sweat redirecting component permits the passage of sweat through the outlet, characterized in that: the apparatus comprises a second sweat redirecting component comprising a second responsive material whose form is configured to change in response to a stimulus, so as to redirect sweat and control an amount of sweat able to be transported to the sweat sensing component via the sweat transport channel, wherein the second sweat redirecting component is positioned at an inlet of the sweat transport channel so as to function as a valve such that, in a first configuration, the form of the second responsive material is such that the second sweat redirecting component prevents the passage of sweat to the sweat sensing component via the sweat transport channel; and, in a second configuration, the form of the second responsive material is such that the second sweat redirecting component permits the passage of sweat to the sweat sensing component via the sweat transport channel. a sweat sensing component for measuring a parameter relating to sweat generated by sweat glands of a subject; a sweat transport channel; and a first sweat redirecting component comprising a first responsive material whose form is configured to change in response to a stimulus, so as to redirect sweat and control an amount of sweat able to be transported to the sweat sensing component via the sweat transport channel; wherein the first sweat redirecting component is positioned at an outlet of the sweat transport channel, such that, in a first configuration, the form of the first responsive material is such that the first sweat redirecting component prevents the passage of sweat through the outlet, and directs the passage of sweat to the sweat sensing component; and, in a second configuration, the form of the first responsive material is such that the first sweat redirecting component permits the passage of sweat through the outlet, characterized in that: the apparatus comprises a second sweat redirecting component comprising a second responsive material whose form is configured to change in response to a stimulus, so as to redirect sweat and control an amount of sweat able to be transported to the sweat sensing component via the sweat transport channel, wherein the second sweat redirecting component is positioned at an inlet of the sweat transport channel so as to function as a valve such that, in a first configuration, the form of the second responsive material is such that the second sweat redirecting component prevents the passage of sweat to the sweat sensing component via the sweat transport channel; and, in a second configuration, the form of the second responsive material is such that the second sweat redirecting component permits the passage of sweat to the sweat sensing component via the sweat transport channel. the apparatus comprises a second sweat redirecting component comprising a second responsive material whose form is configured to change in response to a stimulus, so as to redirect sweat and control an amount of sweat able to be transported to the sweat sensing component via the sweat transport channel, wherein the second sweat redirecting component is positioned at an inlet of the sweat transport channel so as to function as a valve such that, in a first configuration, the form of the second responsive material is such that the second sweat redirecting component prevents the passage of sweat to the sweat sensing component via the sweat transport channel; and, in a second configuration, the form of the second responsive material is such that the second sweat redirecting component permits the passage of sweat to the sweat sensing component via the sweat transport channel.